Parse colors with alpha channel

[stefan-niedermann]

For reference: nextcloud/deck#1545 (comment)

It might be possible to receive color with a format #rgba and #rrggbbaa. We need to make sure that our ColorUtil is capable of parsing a correct color in this cases (+ extend the UnitTests).

[juliushaertl]

We will just drop those for now in deck and apply the rgb values there, since both the frontend and database of deck currently only support plain colors without an alpha channel. However for the future it might make sense to already have this available in the app 😉

[stefan-niedermann]

Yeah, we get some very strange inputs here, while Nextcloud returns a format like #123456, the Deck app returns it without leading #, like 123456. In some weird cases, we also get formats like #123 from Nextcloud or 123 from Deck.

This tiny thing can break the whole sync (this usually pops up as an error, but when importing an account the very first time it can prevent the import at all). Therefore we have a util class and some unit tests to parse a color as good as possible.

I now added a simple case to strip all alpha information for now, so this will definitely make no issues in the near future 😉