Allow replacing GitList's title by another defined in config.ini

As I set up many GitLists, I thought it was a good idea to define a title shown on the top instead of GitList's so I can make the difference easier between each of them.

The title can be defined in config.php and will be also shown in the browser's tab. If it isn't given, "GitList" will be defined by default.

![capture d cran de 2014-06-30 17 33 34](https://cloud.githubusercontent.com/assets/930282/3431619/21580714-006c-11e4-8dc0-1e6546761204.png)

![capture d cran de 2014-06-30 17 36 55](https://cloud.githubusercontent.com/assets/930282/3431648/6f4a5ab2-006c-11e4-84a1-ea911e1f2888.png)