Expression support, including ChangeVar effect
 - Can parse, evaluate and serialize strongly-typed expressions
 - Implements most common operations (easily extensible)
 - Caches constant results to avoid re-evaluation
 - Throws nice exceptions to complain about runtime evaluation problems

Expressions can be built by parsing a lisp-like representation
(see Parser.parse()) or composing Literals, VariableRefs, and Operations

Expressions are evaluated by calling evaluate() on a given VarsContext
Added RecentProjects widget.
Added actions to move, rotate and scale objects in the scene editor
Some improvements in transformations. Still needs work
Improvements to scale transformation
Changed InitialScreen's layout.
Added correct Project parsing from .json.
Added project title and description when creating a new game.
Small changes.
Added columns layout; added default options panel
Added RecentProjects widget.
Changed InitialScreen's layout.
Added correct Project parsing from .json.
Added project title and description when creating a new game.
Merge branch 'master' of https://github.com/e-ucm/ead into RecentProjectsWidget
Used EditorAssets to parse Json attributes.
Merge branch 'RecentProjectsWidget'
Added new strings
Added StyleName for OptionPanel
Added OptionsWidgetPanel