Added SaltStackMaster entity

- Master entity framework is in place
- Tasks to install master and minion available
- Config templates for /etc/salt files for master and minion
- SaltConfig with some configuration keys for minions
Merge branch 'saltstack' of github.com:grkvlt/brooklyn-central into saltstack

* 'saltstack' of github.com:grkvlt/brooklyn-central:
  Adding salt support (and postgres impl)

Conflicts:
	software/base/src/main/java/brooklyn/entity/salt/SaltConfig.java
Modified SaltStack to use masterless minion configuration initially
Add masterless mode configuration key for Salt
Tidy up code