Global error handler and possible bug fix.

I have added a global error handler to catch unhandled exception when ByteFlood is compiled in Release configuration (`DEBUG` constant not defined).

Screenshot:
![screenshot](https://cloud.githubusercontent.com/assets/2142305/4037199/4f38d526-2ca1-11e4-91ef-9893f4f4ef3a.gif)

In case of sever errors, this error handler try to save the state before closing the application (it's going to close either way, but it's nice to close it while saving settings and not displaying "byteflood.exe has crashed" message). Otherwise the use may continue using the program.

Also this commit https://github.com/diantahoc/byteflood/commit/c7f28c19254282ad11700bb8bb7fe7ea48740949 may fix issue https://github.com/hexafluoride/byteflood/issues/22