Spring clean up

Some minor modifications.

* Changed .gitignore according to recommendations for directory-based IntelliJ project ([found here](https://intellij-support.jetbrains.com/entries/23393067)).

* Created separate git repository for TTD dependencies ([here](http://github.com/fuuuu/TTD.Dependencies.git)), and added submodule to main project. Now binary files are available, but not included in the main project.