Bugfix: Allow support for screen types with extremely long full type names

Because the screen identifier is later used to build a filename, extremely long type names (such as those from generic types) end up exceeding the 260 char limit on windows and tend to crash a test when disposing a ScreenRepository.

The test is a little ugly (relies on knowledge of the WindowItemsMap internals) as in the current implementation, it's essentially an integration issue between the ID generated by the ScreenRepository and the filename generated in WindowItemsMap.

A couple of approaches that could allow for this issue to be managed at a unit test level;
 * Changing the Identifier type on InitializeOption from string to Guid
 * Changing the Identifier type on InitializeOption from string to Type