move app navigation to top bar, much cleaner and more room for the app

DO NOT MERGE THIS IN YET

Just a first draft of what moving the app navigation into the top bar might feel and work like. I think it’s a fundamental improvement over the current design because it
* combines the »global« stuff into one bar – it’s less important and shouldn’t take up so much space
* feels lighter because you don’t always have the 2 angle bars, only the top bar
* gives more room to app and content – very important because each app is a full-fledged program in itself. It should be given room.
* makes it much easier to distinguish what belongs to the app and what doesn’t – easier to focus on the work at hand.
* sensibly uses the space in the header
* also solves the strange color difference problem we had with the header and navigation ;)
* makes it easier for the apps to be displayed chromeless because there’s only top whitespace now

Try it out yourself! Or check out the screenshots. They are taken with my 12" 1280*800 Chromebook so you see it works very well even with smaller screens/resolutions, and lots of apps fit in there:

Files currently:
![ownCloud nav old Files](https://f.cloud.github.com/assets/925062/395614/dc2e1b38-a806-11e2-90d4-c1bb51ec70e4.png)
Files with the new design:
![ownCloud nav new Files](https://f.cloud.github.com/assets/925062/395616/dc6eb134-a806-11e2-9465-cbfdc2741243.png)
You see it allows much more room for the app itself. This is even more important as Files will/should also get a sidebar (#1936).

Now an example with an app which already has a sidebar. Currently that feels strange because there are 2 left hand navigation bars:
![ownCloud nav old Notes](https://f.cloud.github.com/assets/925062/395617/dca7c0f0-a806-11e2-859b-f655b89f442a.png)
Now it’s much simpler:
![ownCloud nav new Notes](https://f.cloud.github.com/assets/925062/395615/dc6d5f00-a806-11e2-944d-16995ec8a0d6.png)
Many apps already have this left-hand navigation (Contacts, News, Notes, Bookmarks, Tasks, Music, Mail) and we want to introduce it for some other apps too (Files, Calendar, …). We have default styles for that in core already which are used by Notes and News.


Funnily enough, even with the search bar and username there, the navigation overflows earlier with the left bar than it does with the new design. In case of overflow there will _not_ be a horizontal scrollbar (hope you didn’t think I planned that ;) but rather a »more« entry with a dot-dot-dot icon which then opens a popover showing the remaining apps. This is similar to what Google+ does, or the Android top bar. Although, it’s very unlikely to overflow at all as you see from the above screenshots.

@karlitschek hope that sufficiently explains why I think it’s a necessary change, not just an opinion or redesigning for the sake of it. ;)

@MTRichards @Raydiation @raghunayyar @butonic: What do you think?

Check this out BUT PLEASE DO NOT MERGE IT IN YET!