Efficient rendering of vector-based shapes and lines

- Stages replaced with EditorStage, in charge of a second ShapeRenderer pass
  (similar to the original SpriteBatch pass)
- Actors that wish to draw vector-based in this second pass must implement
  ShapeDrawable
- Replaced all "scaled empty boxes" with a 1 px border rectangle
- Fixes #148 (object-handles resizing themselves)
- Accesses Group's transforms to avoid additional transform matrix creation
Added save point to commands (to check if there is pending changes to be saved)
partial changes message bubble
Revert "partial changes message bubble"

This reverts commit 84035a9c462c2c45d303e017750103c455743309.
Implementation of a simple dialog for showing information messages
Adaption of dialog and diallog controller for supporting modal dialogs and show/hide minize button
Test and main class
Fixed CombinedAction args valitity check.
Merge pull request #296 from RotaruDan/combinedActionFix

Fixed CombinedAction args valitity check.
Merge pull request #290 from manuel-freire/shape-rendering

Efficient rendering of vector-based shapes and lines
Modifications related pull request made by Angel Serrano
Merge pull request #295 from angeldelblanco/info-dialog

Info dialog
Added UITest showing basic widgets
Mockup now loads it's own skin initially.
Removed unused check during shapeRenderer pass.
Fixed small Widget positioning bug.
Avoided duplicated code improving ApplicationAssets constructor.
Merge pull request #299 from RotaruDan/mockupFixes

Some Mockup adjustments after the recent prs.
Fixed bug in mode painted of the scene edition
Merge pull request #302 from RotaruDan/PaintView2

Fixed bug in scene edition