Remove old mixins

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Add box shadow to issue box

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Change header color in network page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'mixin-cleanup' into 'master'

Mixin cleanup

* Remove old mixins
* add issue box shadow
* change color for network graph box
Backup wiki repo even if the main repo is empty

This fixes a bug where wiki repositories for projects with an empty main
repository would not get backed up.
Merge branch 'backup_wiki_skip_bug' into 'master'

Fix wiki backup skip bug