Introduces two new settings:
* `MISP.self_update` allows to enable/disable the GUI button for MISP self-update on the Diagnostics page.
* `MISP.online_version_check` allows to enable/disable the online MISP version check when loading the Diagnostics page.
These settings are useful for 1. container installations that should
not be updated using self-update, and 2. installation that have no
direct or proxy internet access.
There are also improvements on the Diagnostics page, primarily the MISP
version area. Font color has been replace with classes, this allows the
use of the `bold` class, not just colors, and possible combination with
the red/green/orange colour classes.
The info/status/warning/error texts have been changed to take into
account the status of `MISP.self_update` and
`MISP.online_version_check`.