PreferencesMenu updated: can select thread numbers, and whether one or
all files are selected.

GUI updated: some bugfixing
Can now save multiple files:
if only one file is opened or the user set workOnAllFiles to false the
output name will look like "result.png"

else the output name will be like "result[0].png", "result[1].png", and
so on.
In this case the user only has to type the core name of the file (ie
here "result")

Modified files: FileBrowser and GUI
Merge branch 'master' of https://github.com/oPinon/PhotoWork.git