Bug: unverified mod makes 0 ad mod downloader unable to function.

[nani]

Steps to reproduce:

1) Be a user in mod.io with an already verified and public mod.
2) Upload a new version of your mod but without verification.
3) Set that unverified mod as the current active release.
4) Go to 0ad mod downloader page and see as you get an "metadata_blob not decode as an object" error.
5) Make again (with mod.io) the verified mod the current active release to stop getting the error.

[Silier]

In 23821:

Stop failing if mod is broken and display invalid mods in downloader [Mod Io]

If one mod is not signed or broken in any other way, mod.io downloader fails and does not display any mod.
The problem with unsigned mod is that its metadata are empty.

That means one cannot break mod io downloader with mods having invalid data.

mark mod as invalid and display in list as disabled and display reason instead description to not spam ugly error messages on screen as this is not error by the game but of the moder
report failed signatures back to list of mods
fail if property is not set using strict mode when getting from js
check in js for undefined values

Allow to filter only valid mods.

Differential Revision: ​https://code.wildfiregames.com/D2114
Reviewed by: @Itms
Fixes: #5459