Implemented support for the 'monero:' protocol

- Added an option to show QR codes in large (just double-click on them)
- Improved the code for being a single-instanced application
- Updated the QR code generator's URI scheme
- Changed the default behavior of double-clicking on a contact in the Address book (it shows the QR code generation window from now)
- Fixed some localization-related issues (punctuation characters should now be all right)
- Deprecated simpleminer's path setting