Update for public version

- Added About window.
- Added saving of username and syntax when application is closed, will be
  set again upon loading the application again.
- Added icons for the paste and about buttons
  These are based on FontAwesome font which is licensed under OFL (Open
  Font License) and is free to distribute.
- Removed PasteBin service, too much restriction on the pastes allowed per
  day.

Signed-off-by: Steven Downer <grinch@outlook.com>