Some refactoring of text display widgets:
- renamed some methods/classes with better names + some consistency (no more print, setTxt and setText that do exactly same thing)
- TextBox now contains label widget instead of inheriting it
- smooth scrolling support (up/down buttons still scroll one line)

git-svn-id: http://svn.code.sf.net/p/vcmi/code/trunk/@3518 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834