TagsComponent and TagsProcessor addedAdding a TagsProcessor and TagsComponent for processing tags. The Tags component was already available in the model but not in engine
Some minor changes in VarsContext so complex types (e.g. Entity) can be used for declaring variables
VariablesSystem updated so a "$this" entity variable can be used to set context.
Other systems and ChangeVarExecutor had to be updated since they use VariablesSystem
HasTag operator added to expressions. Test updated
@anserran comments addressed
Schema
Executor and initialization
Test
(DO NOT NEED TO REVIEW) bindings
Bad formatting in these three classes breaks my nerve
Merge pull request #380 from jtorrente/formatting

Bad formatting in these three classes breaks my nerve
Merge pull request #376 from jtorrente/expression-improvements

Improvements to expressions and variables system
RemoveComponentExecutor adapted so it can read model component alias and convert them to engine component classes.
Initialization and test updated
Fix #368
Fix #341
Merge pull request #382 from jtorrente/issue-368

Fixes issues #368 and #341
Merge pull request #379 from jtorrente/removecomponent

Remove component effect
Small bug fix in abstract widget test
Merge pull request #386 from anserran/tabs

Small bug fix in abstract widget test