5.1 sandbox data-access refactor into 2 new sub-projects: core and api

- 2 new sub-projects: core and api
- core ivy dependencies include api
- build process places both jars in generated zip and places api in core’s lib folder
- build process (ant install) also copies api jar to biserver’s tomcat WEB-INF/lib (see build.properties in root)
- renamed packages as suggested (ex: from org.pentaho.platform.dataaccess.catalog.api(impl).* to org.pentaho.platform.dataaccess.api(impl).catalog.*)
- applied code-style check
- updated plugin.spring.xml paths accordingly
- installed plugin on a biserver (ant install) and tested one of its endpoints (/pentaho/plugin/data-access-v2/api/metadataDA/getDatasourcePermissions)