This commit adds support for most common accessibility
methods/attributes to the OakTextView component. In user's language,
VoiceOver users (i.e. blind and visually impaired users) can now use
TextMate to read and write text.
A few less used accessibility attributes remain to be supported -
especially AttributedStringForRange and StyleRangeForIndex which should
allow blind users to e.g. see and seek for spelling errors in text.