Removed lazy param and isConstant from operations
Fix camera casts

it is natural to write viewport resolutions in pixels; however, viewport
calculations are done in float coordinates. This fixes, for example,
the CoolDemo
Reverts "cannot change reserved vars" rule. This should be enforced
in the editor (when creating user vars), but not in the engine.

The current restriction breaks runtime language change via effects.
Merge pull request #643 from manuel-freire/fix-camera-casts

Fix camera casts
All tests refactored (can be skipped in review, probably)
Refactor in engine construction process
Needed for later commits
Parameter to schema
Added parameters to components
Added parameters to effects
Added TextComponent, as generic class to deal with expressions
LabelComponent supports expressions
TextButton supports expressions
Updated initializer
Simplified methods to create icons buttons
Refactor in buttons creation
Fix bug in IconButton
Bug fix in ReorderSelection
Bug fixes in camera and debugview
Merge pull request #642 from anserran/opsimpl

Removed lazy param and isConstant from operations
Merge pull request #647 from anserran/sbf

Bug fixes related to enable state in icon buttons