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 icon, with a hover state.

This could probably use some more tweaks, but overall I think it looks pretty reasonable?

Test Plan: {F35897}

Reviewers: chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D5340