Fixes to wxGA_TEXT and wxGA_PROGRESS documentation.

Correct the HTML output format for wxGA_PROGRESS, it was indented incorrectly
because Doxygen appears to need a blank line (i.e. end of paragraph) after a
"@since".

Also improve the wording of the styles descriptions a little.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78081 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775