Transformed the preservation process of shape effects to be able to
store more than one effect. For that we:

* Created the Effect struct and added a vector member to the
  EffectProperties struct.
* Changed the shadow effect to use the new Effect struct,
  EffectShadowProperties struct is preserved because the direction
  field still has some use but we should remove it.
* Changed the structure of the grab bag to store more than one effect.
* Modified an existing unit test to check shapes with several effects.

Change-Id: I0dd908fa1d9578827c02ef6272fc9e2b914391be