REST Call for fetching commits in a branch

This pull requests provides some changes for the support for branch selection and pagination in the commit overview (the project page).

First of all, a List of commits is not required to be sent with the `DetailedRepositoryModel` anymore. Devhub picks a branch it prefers, and then retrieves
the `DetailedBranchModel`. The `DetailedBranchModel` contains a list of commits. This list of commits can be filtered (skip and limit values). The values along
with the actual amount of commits are stored in the `Pagination` object in the `DetailedBranchModel`, to provide Devhub with all information needed for proper
pagination.

The `RepositoriesMock` had to be changed a lot as well due to these changes. This is because it was misusing the recent commits within `DetailedRepositoryModel`
to store the actual commits in. For the `RepositoriesMock`, `DetailedRepositoryModel` is now replaced for a more advanced `MockedRepositoryModel`, which contains
a list of `CommitModel`s  and some sugar methods to actually store tags, branches and commits in the mock. To bind these commits to a branch, I armoured the 
`RepositoriesMock` with a small commit walker.

**Maven build result**

```
[INFO] Installing C:\Users\Jan-Willem.GMELIGMEYLING\git\git-server\git-client\pom.xml to C:\Users\Jan-Willem.GMELIGMEYLING\.m2\repository\nl\tudelft\ewi\git\git-client\0.0.1-SNAPSHOT\git-client-0.0.1-
SNAPSHOT.pom
[INFO] Installing C:\Users\Jan-Willem.GMELIGMEYLING\git\git-server\git-client\target\git-client-0.0.1-SNAPSHOT-tests.jar to C:\Users\Jan-Willem.GMELIGMEYLING\.m2\repository\nl\tudelft\ewi\git\git-clie
nt\0.0.1-SNAPSHOT\git-client-0.0.1-SNAPSHOT-tests.jar
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] git-server-parent .................................. SUCCESS [  0.232 s]
[INFO] git-models ......................................... SUCCESS [  1.851 s]
[INFO] git-server ......................................... SUCCESS [  3.147 s]
[INFO] git-client ......................................... SUCCESS [  1.192 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.534 s
[INFO] Finished at: 2014-07-19T03:09:46+02:00
[INFO] Final Memory: 23M/133M
[INFO] ------------------------------------------------------------------------
```