fix date formatting tests that break with offset timezones by providing explicit javascript dates to test against
support for inline grouping
when a group is expanded, the line items will now be shown directly
underneath the group item instead of going to a separate screen with
only that group. to accomplish this, we have a new group pager that sits
in front of the collection and manages the rows returned. see the
group_pager for details.
remove Tent.Data.GroupingSupport as it is no longer used, cleanup some group_pager code according to comments on PR393 code review, extract group and subgroup expand/collapse arrows to css class along with the background colors for subgroups
unit tests for new grid grouping on frontend, update sinon to latest
add null check on grid content for group header formatting, merge subgroup background css to single entry