Restructure project sidebar and add more icons.

I moved the repository stuff down (including the clone bar), and the project/contribution stuff up. I also added more icons, to the sidebar and tabs on other pages.

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![Screen_Shot_2015-05-12_at_10.29.36](https://gitlab.com/gitlab-org/gitlab-ce/uploads/ada4a77a07913571e5ac4f00fdd182b9/Screen_Shot_2015-05-12_at_10.29.36.png)

See merge request !633