postgres: graphical query builder

[wip]added empty list cta to team list

added Bitcoin as a currency option

* Reopen log files after receiving a SIGHUP signal

Implements a system signals listener in log.FileLogWriter.

After receiving a SIGHUP signal from the system, the listener will close the current log file and then open it again.

The listener will finishes after receiving a SIGINT, SIGKILL or SIGTERM signal.

Closes grafana/grafana#2497

* Move the SIGHUP handling to the main file

response.ContentLength might be invalid if the http response
is chunked.

fixes #13079

[skip ci]

Alerting notification reminder

* updated rules for variable name and fixed files that didn't follow new rules

* fixed test so it uses new rule

* made exceptions to rule in interval_variable

* word fix

support >> supports 
says >> ways

* : for emphasis

Merge branch 'postgres-query-builder' of git+ssh://github.com/svenklemm/grafana into postgres-query-builder