Allow fontawesome icons to be used as application logos (#2853)

This MR changes the behavior of applications logo.

When it contains a dot (.), nothing changes, the logo is considered to be an image file.

When it doesn't contain a dot, it is treated as a Font Awesome icons, with special template processing.

Example, replacing default LLNG icons with FA icons:

Manager UI has been extended:

with dot: without dot:

a help text links to the list of Font Awesome v4 icons:

Implementing this change required adding font awesome to the manager.

I did not update Font-Awesome version because the version provided by debian is stuck at 4.7.0, we should discuss this separately. Of course, a custom portal theme could use any higher version, or even a different icon pack