Alias for parameterized feh image viewer: iv.
Moved static args to env var OSD_OPTIONS.
New probe action to query if a connection is up.
Disabled delegation to mailcap handler.

Probably I will remove that handler script in the near future.
It has become obsolete in the meantime.
Modernized to meet my current requirements.

* added the VB Macro code to have it all in one place,
  it can be printed with -m
* added a help screen
There are some incompatible changes:
* replaced zenity dialogs with notify-send ("bubbles")
* acknowledgement by calling the script with -x
* added check_work_net to the prerequisites