Translation of the MIDI import panel

This is translation for the MIDI import panel operations and track labels.
There are two new contexts: "MIDI import operations" and "MIDI import track list".

*.ts file fragment:
https://docs.google.com/document/d/1oYhtVo_WXCmgTR4V7lWjLT3tGa0LWLiA98CjhTcaI8o/edit?usp=sharing

Test run showed that it works correctly:
https://drive.google.com/file/d/0B5alKuFoSol2dHpsQmJKRVE5TTg/edit?usp=sharing

(Quantization, Track were picked for example translation to Russian).

I checked later, even "compound" strings (like %1 arg) are translated.