Add new constructor to ManageablePosition that takes unique ID, quantity and a bundle of security IDs.
Alter PositionMaster so it extends AbstractChangeProvidingMaster<PositionDocument>, rather than extending
AbstractMaster<PositionDocument> and ChangeProvider individually; this brings it in line with other masters.
Separate out all the caching master tests that are common across all the masters into EHCachingMasterTest, so
that they are executed only once; AbstractEHCachingMasterTest still provides functionality common to all caching
master tests, including EHCachingMasterTests.
Alter PortfolioMaster so it extends AbstractChangeProvidingMaster<PortfolioDocument>, rather than extending
AbstractMaster<PortfolioDocument> and ChangeProvider individually; this brings it in line with other masters.
Initial commit of caching masters & tests for config, exchange, holiday, portfolio, position, region, security
& user; currently incomplete. Each of these classes will only implement the specialised methods/tests for that
specific master; the common parts are implemented in AbstractEHCachingMaster, and tested in EHCachingMasterTest.