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fix and test getNext/PreviousElement
go to next/prev element in joker
Merge branch 'master' of https://github.com/Phonations/Joker

# By ThomasAy
# Via Martin Delille (3) and ThomasAy (1)
* 'master' of https://github.com/Phonations/Joker:
  Add desable button if list empty & refacto
  clean up
  Drop to window to open file is ok
  works with video file
  cleanup
  Works fine
  The ui is functionnal
  First try with open recent, works a litllte

Conflicts:
	app/Joker/MainWindow.cpp
	app/Joker/MainWindow.h
	app/Joker/MainWindow.ui
remove flooding log in PhVideo