Added viewport size values to the Editor.
They aren't used in the Desktop version although they are needed for the Mockup in order to achieve resolution independence in all the devices.
For example, let's say I want my Widget to have a width equal to the 20% of the total screen I would set it's preferred width to Editor.getWidth() * 0.2f;
Since we use a virtual viewport in Mockup they replace the traditional Gdx.graphics.getWidth()/Gdx.graphics.getHeight().
Changed Mockup widget to be resolution independent.
Some code cleaning.
Merge branch 'ViewportWidthHeight' of https://github.com/e-ucm/ead into ViewportWidthHeight
Removed width and height constants from Editor, now uses platform-specific size.
Merge branch 'master' of https://github.com/e-ucm/ead into ViewportWidthHeight
Merge pull request #83 from e-ucm/ViewportWidthHeight

Viewport width height and some code cleaning.