Impress App New Styles

Impress App wasn't working well with the recent upgrades of the new ownCloud 5. Had to rewrite it's most of it's styles. To maintain uniformity, I tried my best it looks similar to files but added a few of my own changes too. Please confirm! :)
Reference : https://github.com/owncloud/apps/issues/548
cc @karlitschek and @jancborchardt