clone repository, remote picker and history improvement

List of changes:

- Added **clone repository** feature, it lets users clone an existing repository into the project folder
- Added **remote picker** feature, it lets users pick the remote to use on push/pull
- Now **history** button has two labels "Show history" and "Hide history" depending by the state

![image](https://f.cloud.github.com/assets/5382443/2293026/3368a100-a065-11e3-9269-40b10ad6de0a.png)

![image](https://f.cloud.github.com/assets/5382443/2293030/4079ba6e-a065-11e3-9e6b-ad12d84a083c.png)


Currently the **remote picker** doesn't allow to add new remotes but I'd like to implement it later.

Hope everything it's okay.