Add JMX attribute sensor entity initialiser
Set sensible defaults for senor addition
Tidy up sensor addition code
Add type coercion to added SSH command sensors
Added location definition attribute to location owner
This closes #315

* github/pr/315:
  Added location definition attribute to location owner
This closes #311

* github/pr/311:
  Add type coercion to added SSH command sensors
  Tidy up sensor addition code
  Set sensible defaults for senor addition
  Add JMX attribute sensor entity initialiser