New pull requests for filter extension to Exhibit plugin

[naeemmuhammad]

Currently, in admin view, exhibits from all users are shown. There is no support in Exhibit plugin for users to see their own exhibits only. In the context of Espace project we need a filter to let users filter their own exhibits. To provide such support we have implemented 'owner' filter and made a pull request( (omeka/plugin-ExhibitBuilder#81). Owner of the Exhibit plugin wants separate pull requests for various modifications needed to introduce this filter.