Better colors generator

[skjnldsv]

A better color generator, with pastel colors and a brightness check to prevent illisible text.

I didn't liked the colors on the contacts app, so i made a color generator using the hsl wheel and a different angle base on the contact uid. I use a hsl to rgb function found online (too simple to bother coding the same function on my own) and a basic common brightness algorithm.

[mention-bot]

By analyzing the blame information on this pull request, we identified @Henni to be a potential reviewer

[irgendwie]

@skjnldsv Would you mind squashing your last commit? (https://ariejan.net/2011/07/05/git-squash-your-latests-commits-into-one/)
LGTM 👍

[skjnldsv]

@irgendwie Good here?

[jancborchardt]

@skjnldsv can you directly modify the color generator in core please? See https://github.com/owncloud/core/blob/master/core/js/placeholder.js#L54-L58 :)

Because we should use the same color scheme across ownCloud, especially for the placeholders. When I share something with a person, the placeholder should be the same as in the Contacts app for that person.

[skjnldsv]

Dammit, why no one said that before? :p

[jancborchardt]

@skjnldsv yeah, sorry bout that. ;) Would still be cool if you could do that. :)

[skjnldsv]

Too busy crying ;)
Will do in a moment, i'm working on the header inputs now.

[jancborchardt]

:D Welcome to open source development ;D

[skjnldsv]

Wait a minute, I didn't realised. You want to use the core generator in the contacts app, or my generator in core?
If you were considering the second option, please see #306

[jancborchardt]

@skjnldsv a combination of both: Ideally your improvements are done to the core generator, and then we use the core generator in Contacts. (Because the core generator is also used everywhere else.)