Add multi-select actions and visual improvements to the dashboard.
This is the first big update we've had to the dashboard in some time.
First, it adds support for multiple selection of review requests, and

actions that can be invoked for those that are selected. The actions

right now are limited to closing review requests, but more can be added

down the road.
The action pane appears over the sidebar. It's in a darker color and is

semi-transparent (but only barely). It goes away when no review requests

are selected.
This also makes the dashboard take up the full height of the page

(excluding some padding and the content above it). The rows of entries

scroll now, instead of having to scroll the entire page. With the new

changes to datagrids in Djblets, the rows are able to scroll without

affecting the header, meaning you can always see what column represents

what cell.

Tested in Chrome, Firefox, IE10, and IE 7/8/9 in IE10's compatibility modes.
Tested selecting and unselecting different numbers of review requests.
Tested selecting/unselecting all review requests.
Tested that changing columns or performing other operations that may mess

with selection (due to reloading the contents of the datagrid) cleared the

selection, removing the actions pane.
Tested closing review requests as discarded and as submitted, individually

and as groups.
Cleared the entire dashboard in one go with a close operation.
Tested that after performing an action, the contents of the dashboard

reloaded.
Tested with a review request I didn't have permission to close. Saw it handle

it gracefully and notify me that one couldn't be closed in the results dialog.