* [RAPPS] move settings-related stuff to a separate file
* [RAPPS] refactor reg read/write
* [RAPPS] add params for Load/SaveSettings, no longer use global vars
- Add download source in settings dialog, and apply it when download .cab file
- Now user should specify full rappmgr.cab URL
- Check if URL is vaild in settings dialog
- Move source settings to the end of struct (will refactor settings to one value per option later)