py3: numerous bug fixes & subprocess calls changed
* Subprocess is only called through subprocess.call() or subprocess.check_output() now. Proper syntax is now used to separate arguments in subprocess calls.
* Fix deadbeef PID detection: use pgrep to detect deadbeef's PID, regardless of the name of the deadbeef process (deadbeef-gtkui, deadbeef-main, etc).
* Fix inaccurate launch/close print statements: mostly due to an incorrect handling of both call_db functions.
* Fix numerous random crashes. Some might still happen, though that's unlikely now.