Project file conversion from version 2 -> 3

Traverso 0.40.0 - 0.41.x is able to open project files with version 2.
From Traverso >= 0.42.0 it needs to be at version 3.

The conversion of the Project will consist of the following actions:

• Convert the project.tpf file to use universal sample rate for position and length, as opposed to using a fixed samplerate
• For performance reasons it was decided to start using interleaved audio files. For each recorded stereo file the 2 mono files will be merged into 1 stereo file.
  NOTE: This can take a long time for large files!