This required some changes to the framework:

* Init-/DeInitVCL is no longer done per individual test in BootstrapFixture, but
  once per CppunitTest invocation in a new vclbootstrapprotector (similarly to
  the exisiting unobootstrapprotector).  CppunitTests that need VCL now need to
  declare gb_CppunitTest_use_vcl.

* For things to work properly, the UNO component context needs to be disposed
  from within DeInitVCL (cf. Desktop's Application::DeInit called from
  DeInitVCL).  The easiest solution was to introduce an
  Application::setDeInitHook (where the hook is called from DeInitVCL)
  specifically for vclbootstrapprotector to call.

* PythonTests don't (yet) call DeInitVCL; they still hook into
  BootstrapFixture's original test_init functionality (to call InitVCL), and do
  not make use of the vclbootstrapprotector.

Change-Id: I4f3a3c75db30b58c1cd49d81c51db14902ed68b2