R1:018de5dec742

Use ObjectItemListView for Maniphest

Summary:
This isn't quite complete, but everything else is technical cleanup. Broadly:

- Removed checkboxes. Selected state is now indicated with CSS, and toggled with shift-click. When nothing is selected, the text reads "Shift-Click Tasks to Select" to let users discover this feature.
- Updated drag-to-reorder code to work with ObjectItemListView.
- Closed/resolved is now shown with a grey footer icon.
- Assigned is now shown with a user profile image handle…