Added apache-license-2.0.txt, lgpl-3.0.txt, and mysql-license.txt
Issue: MIRTH-2958
It was decided that we will remove the thirdparty license folder for now and in a future release, add a single third-party license file that contains all required license information for third party libraries/code that we use, similar to how Oracle does with Java itself.
Issue: MIRTH-2958
Added text to About dialog for attribution for the xpp3 library - required by it's license.

Updated the url for the silk icon set to point directly to the Silk iconset page, as requested by the author.
Issue: MIRTH-2958
Appended license headers.
MIRTH-2960: Fixed an issue with the byte abbreviation list's transfer handler that caused "FFFFFFFF" to show up. Also limited the abbreviations in the list to go up to 0x7F instead of 0xFF.