Make Vocaluxe buildable and playable on GNU/Linux

Build with MonoDevelop or make.
Summary of the biggest changes:

* Correct for case differences between System.Data.SQLite and
  Mono.Data.Sqlite
* Exclude Direct3D and DirectSound from linux builds
* Provide linux versions of some windows-specific build events
* Exclude VocaluxeTests from linux builds so xbuild will work
* Add ability to build the native PitchTracker on linux
* Fix some problems with acinerella module
* Fix some windows-specific dependency checks that fail on linux
* Set OpenGL color format to 24-bit on linux

HowToBuildLinux.md

@@ -0,0 +1,4 @@
+# Build Vocaluxe - HowTo (Linux)
+
+* Clone the repository (see [this](https://github.com/Vocaluxe/Vocaluxe/blob/develop/HowToBuildWin.md) for help)
+* Navigate to the cloned repository and execute `make`. Make sure that all dependencies are installed and the process completes without errors.