Add Spinboxes

* Single Step added as tick to the slider
* Collapsible Widgets
Merge remote-tracking branch 'chrysteljuan/gui-improvement' into cleanup

* chrysteljuan/gui-improvement:
  Add Spinboxes
Try to fix issue on Windows

* when type shift+D
Don't search default path when JsonCpp_DIR is provided

If a JsonCpp is present in a default path on the computer,
find_package(JsonCpp) was selecting this one instead of the path
pointed by JsonCpp_DIR.
Merge remote-tracking branch 'chrysteljuan/gui-improvement'

* chrysteljuan/gui-improvement:
  Try to fix issue on Windows
  Add Spinboxes
Merge branch '42-fix-jsoncpp-find_package-with-system-lib'

* 42-fix-jsoncpp-find_package-with-system-lib:
  Don't search default path when JsonCpp_DIR is provided
Fix display states

When typing the "Shift+d" key, the display states are as follows:
 OFF -> ON -> into TextEdit -> OFF without widgets -> ON without widgets
Merge branch 'fix-display-states'

* fix-display-states:
  Fix display states
Fix focus

Listen to pressed keys and propagate to slice view
Closes #45
Merge branch '45-fix-focus'

* 45-fix-focus:
  Fix focus
Fix the size of the dialog

Closes #33
Merge branch '33-fix-sizing'

* 33-fix-sizing:
  Fix the size of the dialog
Use pimpl in QtSlicer
Factorize code in QtSlicer
Rename QtSlicer into QtImageViewer
Cleanup QtSliceControlsWidget

Move the slider/spinbox setup into QtSliceControlsWidget.
Merge branch 'code-cleanup'

* code-cleanup:
  Cleanup QtSliceControlsWidget
  Rename QtSlicer into QtImageViewer
  Factorize code in QtSlicer
  Use pimpl in QtSlicer
Merge branch 'master' of github.com:KitwareMedical/ImageViewer