Tests: Added tests for applying one font style over another.
Remove existing font style before applying new one.
Tests: Added more test cases for deep structures.
Handle the collapsed selection case, when we can't use editor.removeStyle.
Tests: Turns out that insertText is also affected by the ACF - that's because of how the text is being processed.
Tests: Added manual TC.
Tests: Test for correcting the font size.
We need to remove the empty style element because it is visible.

See http://dev.ckeditor.com/ticket/12403#comment:22
Added note about temporality of this fix.
Changelog entry.
Merge branch 't/12403d'