A button to show closed MIDI import panel

The button at the bottom:
https://docs.google.com/file/d/0B5alKuFoSol2cXhYWFJtQ3hZNmc/edit?usp=sharing

== The use case ==
If the user decided to close the MIDI import panel but after that he wanted to open the panel once again (without opening a new MIDI file) and change some import parameters - then this button could help with that.