Us21 quota visualization

User story: *As a user I want to see statistics of my quota both in terms of space and percentage*

The implementation is pretty straightforward. It introduces a new activity and is very simple.

It depends on 
1) https://github.com/owncloud/android-library/pull/44
2) https://github.com/owncloud/android/pull/661


My only doubt is about the possible errors that might be returned. ( https://github.com/owncloudChalmers/android/commit/4a0e71ae6d737cc96e0c9cc57bb2b8006dcb44c4#diff-15 at onRemoteOperationFinish )

Some screenshots:

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051091/957d84be-6c34-11e4-8136-3753b9d619e5.png" align="left" height="350" ></a>

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051092/957df5f2-6c34-11e4-99d8-9d05b35f0578.png" align="left" height="350" ></a>

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051094/9581a4fe-6c34-11e4-9aa0-5d7ff1c317bc.png" align="left" height="350" ></a>

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051093/9580abf8-6c34-11e4-8a84-acb4b0211b96.png" align="left" height="350" ></a>

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051096/9581ff30-6c34-11e4-8f5d-84d9580f6f0b.png" align="left" height="350" ></a>

<a href="url"><img src="https://cloud.githubusercontent.com/assets/2060779/5051095/9581fcf6-6c34-11e4-8eef-b5473d9bb4ac.png" align="left" height="350" ></a>