[SAC] Gitea upgraded to 1.5.1+

[Sandro Santilli]

I've upgraded Gitea to 1.5, we were coming from 1.3.
What the upgrade brings us is:

 - Autocompletion of mentions
 - Reactions (like, smiles etc)
 - .patch and .diff for pull requests (Regina: this may fix Jenkins
   hooks)
 - Pull Request merge options (rebase, squash etc.)
 - Multiple assignees for issues

Plus a ton of other improvements/fixes

Please report any issue that arises from this upgrade.

--strk;