temporary color picker/eyedropper + setTemporaryTool() implement

just press [ALT] key to pick a color
temporary drag (commented how to set any tool temporarily)

@chchwy
Most common shortcuts for temporary tools are added to code until they
can be added to shortcut configuration. if you find convenient to
implement temporary selectors.
Merge pull request #150 from eVoLuTiVeMEDIA/master

temporary color picker/eyedropper + setTemporaryTool() implement