Added new json column for work external identifiers, and changed work
contributors to json data type in postgres.
Implemented storage of work external ids as json.
Added DOI index to work.
Added system exit.
Added default change log to liquibase props.
Added preconditions just in case liquibase is run in different ways, and
so has different filename for changeset.
Pushed up to latest 2.x version of liquibase.
Added script to initialize database, so that can easily be run as
postgres and have liquibase behave consistently to spring/tomcat with
regards to changeset filename.
Fixed so that manually added works are saved as json.
Added comment.
Went back to version 2.0.3 of liquibase as later version seemed to cause
some errors (maybe looked at upgrading to latest 3.x version instead at
some point).
Add license.
Corrected docs.
Merge branch 'master' into storeWorkExtIdsAsJson

Conflicts:
	orcid-persistence/src/main/resources/db-master.xml
Added migration SQL.
Merge branch 'master' into storeWorkExtIdsAsJson
add external identifiers to minimized works
Merge branch 'master' into storeWorkExtIdsAsJson
Merge branch 'master' into storeWorkExtIdsAsJson
Merge pull request #1144 from ORCID/storeWorkExtIdsAsJson

Store work ext ids as json (second pull request)