Refactor the WYSIWYG selenium tests to allow global setUp for all tests

The WYSIWYG tests need setup to be executed before they are all executed, such as login (since they are all executed as admin and one login should be done for all tests to save time) or enabling all the editing features in the wiki preferences before doing any test involving the wysiwyg editor.
Also, the strategy should be to set the skin executor per test suite not to have every test sets its own suite with executor (the test case shouldn't be aware of the skin executor it executes under and the skin executor should be changeable from just one place, for all the wysiwyg test suite).