Signed-off-by: Dirk le Roux <dirk.leroux@gmail.com>

* fix(table): renderes empty date column as '-'

closes #6728

* docs(changelog): add note about closing 6728

closes #6731

ref #6719

closes #6701

closes #6703

Feature/tls client auth

- Three text areas where the user can paste
in the CA Cert (optional), Client Cert
and Client Key.

- Tooltips for Auth checkboxes with brief
descriptions of what With Credentials and
With CA Cert are.

- Adds popover for TLS Auth header too.

- Aligns gf-form elements as labels and
checkboxes were not aligned before.

- Makes CA Cert optional as it is only
needed for self-signed certs.

The tls files are stored as a json blob in the
SecureJsonData field. To update one file, the
json has to be fetched from the db first and
then updated with the cert file that has been
changed.

Also, a change to the dto with flags that are
used in the frontend to show if a file has
been uploaded. For example, if tlsClientKeySet
is set to true then means a file for the
client key is saved in the db. This is to
avoid sending any private data to the frontend.

For self-signed TLS Certificates, authentication
with InsecureSkipVerify set to false then this
error will occur:

x509: certificate signed by unknown authority

The solution is to allow the user to upload the
CA cert as well.

Use a SecureJsonData field for TLS
Client Auth instead of 3 new db
fields. Same model as used for
PluginSettings.

Saves and encrypts the pem file
content rather than just saving
the paths to the cert and key.
This allows for uploading from
the Edit Datasource page in
Grafana.

Extract from pluginsettings class so that the
securejsondata type can be used in the other
classes. Encrypt and decrypt functions
extracted too.

fix(unsaved changes): You now navigate to the intended page after saving in the unsaved changes dialog fixes #6675

* Sort series by yxis by default

* Sort series by yxis by default

* Sort series by yxis by default

ref #6576

fix(server side rendering): Fixed address used when rendering panel via phantomjs and using non default http_addr config, fixes #6660

Fix typo in Basic Concepts