New handle flip implementation.

* Handles flip when:
  - Cross each other.
    They can flip as soon as they cross or when the handles are released.
    Text::Decorator::FlipSelectionHandlesOnCrossEnabled()
  - According the character's direction.
  - If they exceed the boundaries of the decoration area.

* The bounding area is stored in world coords.
  There is no need to store it in actor coords and then transform it on every query.

* Fixes a crash when selection handles are crossed and text is inserted.

Change-Id: Ie0ec8174cb5f34c17f96d7179fcdc3cf05bc2df8
Signed-off-by: Victor Cebollada <v.cebollada@samsung.com>