Misc improvements

* Remove bash scripts and start mailnag python scripts directly
  - Prevents duplicate process names
  - Fixes missing app icon in taskmanager
* Remove background startup functionality
  - Should be handled by modern init systems like systemd
    (see new-style-daemon: http://www.freedesktop.org/software/systemd/man/daemon.html)
  - Enables program termination via CTRL+C when running mailnag in a terminal
  - Doesn't hide the commandline prompt when running with options like --help (reported in issue #87)
  - Fixes wrapping issues in the log output
* Rename mailnagd into mailnag again
* Remove --backround option
* Fix and reorder module imports
* setup.py: patch BIN_DIR in dist_cfg