Rename Form1 to MainWindow.

Create basic GUI skeleton:
 - create search section
 - create results section
 - GUI "backend" is partially implemented (choosing search path)
OpenFileDialog
Merge branch 'master' into Core
Seach button is working now!!
Merge branch 'master'
małe poprawki
Merge branch 'master' of https://github.com/kzemek/PrzeszukiwarkaPlikow