Make list of volunteer opportunities filterable

Displaying all the volunteer opportunities (civicrm/a/#/volunteer/opportunities) an organization has to offer could be overwhelming in some cases. Provide a form to allow end users to filter by date, role, and beneficiary. When new searches are submitted, the URL is updated so that searches may be bookmarked and shared (e.g., civicrm/a/#/volunteer/opportunities?date_start=2015-9-12&date_end=2015-10-12).

The search also accepts one parameter by URL only: project. When used, only the volunteer opportunities in the specified project will show.