Changes

Implement Sentry Importer (#22)
* Implement basic Sentry -> Sentinel imports

* Moved some constants into the SentinelTrait class so they can be used
in range checks during import.
* Added Sentry as a dependency because that's the easiest way to get at
the data. Let Sentry load it, and then read it right out of Sentry's
objects
* Sentry's can now be imported using a command
 Caveats:
* Weapons are not modified, so if a weapon created a specific attack in
Sentry, there is no gurantee the same attack will be used in Sentinel
* Warnings/Greetings are not imported
* Anything not yet supported by sentinel is not imported
  - Guarding non players
  - Various integration targets (towns/nations/factions)

* Switch files from tabs to spaces to respect project whitespace
preference.

* Several minor fixes to Sentry Import

* Correct permission checked
* Add checked permission to plugin.yml
* Reference latest version of sentry
 (commit: 71e8dd0)

Clean up PR'd code
 (commit: 59ffb8c)