Support multiple editors creation in CKEditor bender plugin

[Piotr Jasiun]

It should be possible to create multiple editors in the single tests suit. Also init method should not be locked, if bender.editor property is used.

[Piotr Jasiun]

Changes:

• if bender.editors is defined, multiple editors will be created and available the same way bender.editor works,
• if bender.editorsConfig is defined, it will be merged with config of editors in bender.editors,
• tests with bender.editor/bender.editors now can have init or async:init method,
• setUpEditor method was removed and all tests which used that method were rewritten to bender.editors,
• createTestsForEditors now need editor names instead of instanced as a first parameter.

I also created tests for the new features and run all tests on Chrome, Safari, IE11 and IE8. Everything seems to work fine.

[Piotrek Koszuliński]

Merged to major with ​git:af2b59d.

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