Documented the inner workings of the plugin

This should help with understanding and reading the source code of the
plugin. Which should enable easier and faster patch creations from third
parties!
steam: reorganized information output

This cleans up and condenses the output of the info command.
Refactored enumerator translations

This cleans ups, and unifies similar code blocks.
steam: implemented additional state information

Additional information is available for Steam friends which holds flags
pertaining to the friend state. This includes determining if a friend is
using a web or mobile client as well as big picture mode.
steam: implemented last online information

The last online time is sent via the user summary request, and has been
for quite sometime. The plugin should make use of this timestamp, and
show the user when a friend was last online.