wxStyledTextCtrl can now be built and used when wxUSE_UNICODE==1.

wxStyledTextCtrl can now be built and used when wxUSE_UNICODE==1.
When in unicode mode Scintilla uses UTF-8 internally so the wxSTC
wrapper only needs to convert to/from UTF-8 in the right places.
Still need to figure out to get unicode characters from key/char
events...

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@14693 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775