Minor docs fixes.
Tests: Written test checking whether snapshot is made after 25 chagnes.

Conflicts:
	tests/plugins/undo/keyboard.js
Tests: Improved.
Implemented KeyEventsStack which handle information about key events. Calling type method on uM when keydown exceed 25 for the same keyCode.
Refactoring: Added static KeyEventsStack.getKeyGroup method.
Tests: Added test which check whether undo and redo buttons are in proper state, after undo command.
Fixed issue with wrong UI buttons state. Second approach.
Tests: Added unit tests for getNextImage method.
Tests: Fixes for IE.
Cleaning up and documentation.
Tests: Fixed wrong method call in undo tests setUp which does not exactly set up everything.
Improved created documentation.
Fixed test file name.
Unfortunately we have to avoid bloating production code with long error messages.
Avoid doing things we don't need to do.
Logical simplification.
Vertical spacing and used null insteaf of undefined in place of not passed argument.
Get rid of inputFired in NativeEditingHandler class.
Made some properties and methods static.
Removed hardcoded stack limit. Using increment method in onInput.