VariablesSystem renamed to VariablesManager
VariablesManager is not a System anymore.
Also: some outdated javadoc fixed along the way
VariablesManager added as a field of EngineApplicationListener that is passed down to GameLoader, EngineInitializer, etc.
Accommodating API changes (review not needed)
Package ...engine.systems.variables moved to ...engine.variables (review not needed)
Accessor embedded in VariablesManager
Merge pull request #437 from jtorrente/variablesManager

Variables manager - Fixes #394
Using plain objects for selections instead of Model entities
Fixing format - @manuel-freire owes a beer round
Merge pull request #441 from anserran/master

Fixing format - @manuel-freire owes a beer round
Merge pull request #439 from anserran/selection

Using plain objects for selections instead of Model entities
Added save and bin icons.
Changed the save icon
Improved the tweens panel
Fixed some bugs, typo and junk code. Also added some documentation.