Added remove move or rename function

Functionality was added to access the Dropbox API move function:

- new API Url to access move (API_MOVE_URL)
- new function db_move executing a remove move
- new command rename|move taking the soure/old file and the target/new
file as parameters
Merge pull request #57 from chof747/master

Added handling of DropBox move API command for remote file moving