Added options to display health & location in the tooltips of the TP GUI.

The location displayed is relative (N/S/E/W/S-E/etc. + distance).

Closes #33.
Merge branch 'master' of github.com:pgmann/SpectatorPlus
Added an explicit message if there isn't any potion effect, in the inventory GUI.
Merge branch 'arenaLimit' of https://github.com/pgmann/SpectatorPlus