unify how specs are resolved, including policySpec and enricherSpec, including supporting "policy_type" or "type" as well as the standard "policyType"
(in part because new CAMP spec switches to "_" separator)
add support for referencing initializers in yaml, with tests, plus more cleanup/dedup of how "decoration" types are constructed for entity specs
make MulitLocation obtain across its sub-locations, so that yaml can combine locations with different credentials.
update docs for yaml locations, and for other parts of yaml reference including brooklyn.initializers.
Merge pull request #1379 from ahgittin/yaml-resolution

extend yaml resolution, with more complete docs, including slightly cleaner java, `entity.initializers`, and multi-location obtaining from all sub-locations