adding avatar to project settings page

as per Feature Request:
http://feedback.gitlab.com/forums/176466-general/suggestions/5433454-add-uploadable-project-icons

an icon / avatar for the project.
Logo can be uploaded or included in the project as png, jpg or gif.
If no logo is present a simple colorful one will be generated.

Done so far:
added avatar removal
show project avatar on dashboard, projects page, project page
added rspec and feature tests
added project avatar from repository
new default project icon added
added copying af avatar to forking of project
added generated icon

TODO:
Test must be checked for completion.
UI must be checked for consistency.
(maybe change the words logo / icon => avatar)

Project page with logo:
![screen shot 2014-01-26 at 09 21 27](https://f.cloud.github.com/assets/4224518/2272529/b712b286-9f05-11e3-8f86-72fdcdf8a901.png)

Project settings with logo:
![screen shot 2014-01-25 at 19 53 29](https://f.cloud.github.com/assets/4224518/2272525/b213c450-9f05-11e3-9f80-bbc530b41520.png)

Project settings without logo:
![screen shot 2014-01-26 at 21 15 50](https://f.cloud.github.com/assets/4224518/2272531/bc043878-9f05-11e3-9134-3988200398c2.png)

Project listing with both uploaded and generated logos:
![screen shot 2014-02-26 at 17 39 58](https://f.cloud.github.com/assets/4224518/2272517/9546c8c2-9f05-11e3-8912-fdcb7d2ec6de.png)

Generated icons when no logo is uploaded:
![screen shot 2014-02-26 at 16 06 41](https://f.cloud.github.com/assets/4224518/2272516/95448dbe-9f05-11e3-8417-7d8b6d3423a2.png)
![screen shot 2014-02-26 at 17 40 10](https://f.cloud.github.com/assets/4224518/2272518/95491190-9f05-11e3-9c4f-a5757b551b1d.png)

Use a guard clause instead of wrapping the code inside a conditional expression.