Add do-nothing showInvisibles method to the NullColorizer class.

Leo build: 20140902101220
Attached an eventFilter in the QScintillaWrapper ctor.  This enables key bindings and causes text to stick.
Many unit tests pass with scintilla enabled.  Many fail.
Caution: many unit tests fail: failures may corrupt the .leo file.

Leo build: 20140902101452
Enabled scintilla in unitTest.leo.

Leo build: 20140902102044
Fixed crashers and bugs in QScintillaWrapper.  The widget may be usable for real work, but many unit tests fail.

Leo build: 20140902112520