fix: set lastSeenAt date when creating users to then years in past insteasd of empty date, fixes #9260

Change the query to first select the dashboards, apply the limit then
join with tags. Means the limit will apply to the number of dashboards
returned in the search. The disadvantage is that the query will return
more rows than the limit, no. of dashboards x no. of tags. So hard limit
set to 5000 for all rows.

* add postgresql datasource

* add rest of files for postgres datasource

* fix timeseries query, remove unused code

* consistent naming, refactoring

* s/mysql/postgres/

* s/mysql/postgres/

* couple more tests

* tests for more datatypes

* fix macros for postgres

* add __timeSec macro

* add frontend for postgres datasource

* adjust documentation

* fix formatting

* add proper plugin description

* merge editor changes from mysql

* port changes from mysql datasource

* set proper defaultQuery for postgres

* add time_sec to timeseries query
accept int for value for timeseries query

* revert allowing time_sec and handle int or float values as unix
timestamp for "time" column

* fix tslint error

* handle decimal values in timeseries query

* allow setting sslmode for postgres datasource

* use type switch for handling data types

* fix value for timeseries query

* refactor timeseries queries to make them more flexible

* remove debug statement from inner loop in type conversion

* use plain for loop in getTypedRowData

* fix timeseries queries

* adjust postgres datasource to tsdb refactoring

* adjust postgres datasource to frontend changes

* update lib/pq to latest version

* move type conversion to getTypedRowData

* handle address types cidr, inet and macaddr

* adjust response parser and docs for annotations

* convert unknown types to string

* add documentation for postgres datasource

* add another example query with metric column

* set more helpful default query

* update help text in query editor

* handle NULL in value column of timeseries query

* add __timeGroup macro

* add test for __timeGroup macro

* document __timeGroup and set proper default query for annotations

* fix typos in docs

* add postgres to list of datasources

* add postgres to builtInPlugins

* mysql: refactoring as prep for merging postgres

Refactors out the initialization of the xorm engine and the query logic
for an sql data source.

* mysql: rename refactoring + test update

* postgres:refactor to use SqlEngine(same as mysql)

Refactored to use a common base class with the MySql data source.

Other changes from the original PR:
- Changed time column to be time_sec to allow other time units in the
future and to be the same as MySQL
- Changed integration test to test the main Query method rather than
the private transformToTable method
- Changed the __timeSec macro name to __timeEpoch
- Renamed PostgresExecutor to PostgresQueryEndpoint

Fixes #9209 (the original PR)

* postgres: encrypt password on config page

With some other cosmetic changes to the config page:
- placeholder texts
- reset button for the password after it has been encrypted.
- default value for the sslmode field.

* postgres: change back col name to time from time_sec

* postgres mysql: remove annotation title

Title has been removed from annotations

* postgres: fix images for docs page

* postgres mysql: fix specs

* graph: fix NaN formatting, #9012

* singlestat: prevent null value coloring, #9012, #8404

* timeseries: add tests for #9012 and move test file to TS

exclude dashboard field from snapshot list search

* colorpicker: fix opening error when color is undefined

* colorpicker: replace spectrum picker by new color picker

* colorpicker: remove old spectrum picker directive

* annotations: use tinycolor for working with region colors

Macaron's gzip middleware tries to automatically figure out the content
type for a file when gzipped and seems to mostly fail with plugin
readmes. This change sets the content type to plain text.

Fixes #9344. Ref #5952.

At least in my Postgresql 9.6.5, the old syntax of capitalized queries doesn't work (Linux).<br>
Running with UTF-8 as standard encoding and the ` notations didn't work either, so removed those.