frontend: introduce generics to UICommon (part 1)

Infrastructure part of the introduction of the generics into UICommon.
Changes:
- changed EntityModel and ListModel to be generic
- adjusted UiCommonEditorDriverGenerator to work with generics
- created a <String> version of the EntityModelTextBox. The widgets
  has to have proper generic types and most of them already does.
  Only the ones editing Strings (e.g. EntityModelTextBox) was set as
  <Object>. This patch introduces a generic version of this widgets
  into the .generic subpackage marking the old as depricated.

Change-Id: Ifaa6185e75adfd9405132fce2782f6c7cbc17f7f
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>