SWC-36: add Page entity for wiki support

Signed-off-by: Jay Hodgson <jay.hodgson@sagebase.org>
Merge branch 'develop' of https://github.com/Sage-Bionetworks/Synapse-Repository-Services into develop
Merge pull request #261 from jay-hodgson/develop

SWC-36: add Page entity for wiki support