Sort favorite files first in the list

[jancborchardt]

Favoriting is not very integrated at the moment. Only an indicator, we can do better here.

Better integration without needing to switch to a separate view would be to always sort the favorited items of a the current folder up top.

PR is #302

[AndyScherzinger]

Dev-hint: This should be done for FileDisplayActivity.java so the sorting then needs to incorporate the chosen way of sorting (alphabetical, date, size) as a second order criteria and favorite (yes/no) as a first order criteria.

[ryanwr]

I'll work on this

[AndyScherzinger]

implemented, reviewed and tested, part of the next stable release 1.4.0

[jancborchardt]

@ryanwr @AndyScherzinger awesome! :) Now we should get this in the web interface as well, cc @nextcloud/designers for nextcloud/server#1802