Merge pull request #7 from sevoan/sevoan

little fix for cmakefile.txt support
- ImageViewer: zoom now works
- ImageViewer: fit modes now behave better
- MainWindow: add spacebar shortcut

Signed-off-by: easymodo <easymodofrf@gmail.com>
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a little fix for img centering

Signed-off-by: easymodo <easymodofrf@gmail.com>
Refactoring mapoverlay