Add the version number to the "add sources" page

[desbest]

I have a minor usability tweak to suggest for Selfoss, that should hopefully save you hours of time in handling technical support. How about adding the version number of Selfoss, somewhere on the "add sources" page?

[jtojnar]

I had exactly the same idea and wanted to add it before release but then I forgot about it.

For context, previously the version number was in the sidebar but I dropped it after this discussion.

[dwydler]

I also want the version number back.

[jtojnar]

Hmm, maybe we could open an About page after clicking the selfoss icon in the sidebar.

That way we could show also credits and license information.