[WELCOME]: UI improvements:

[WELCOME]: UI improvements:
- Allow only one running instance of the Welcome application at a time.
- Implement translating \xhhhh hexadecimal character specifications in topic text descriptions.
- Allow using the keyboard for navigating amongst the topics, and ENTER key presses to run the selected topic command.
  <rant> *OF COURSE*, because we are ReactOS *SO* we are *buggy* (well, user32/win32k), keyboard navigation via arrow keys *DOES NOT WORK*!! (only navigation via TAB key do work) 8^(((( </rant>
  This however works OK on Windows.
- Improve topic buttons activation when mouse hovers around above the window, as well as when window activation is lost or regained.
- Change the default text font to Tahoma.
- Don't hardcode white brush, but instead use stock object WHITE_BRUSH. Similarly, don't hardcode text black colour, but instead use the ambient text colour of the system.
- Add keyboard shortcuts to the default topic items.
- Shift the window ID of both the checkbox and the Exit buttons to be below a fixed topic-button base ID.
- In GetLocaleName(), use more explicit returned-variable names (cchRet, because it's a returned string length in character numbers).

svn path=/trunk/; revision=75282