Added subscriber view to Maniphest.

Summary:
People want to see all the tasks they have subscribed to in one
view. A new table was added for this to make queries faster.

Test Plan:
Tested that the view was initially empty. After running the
reindex_maniphest.php script, I saw the correct tasks there. Added
myself as a subscriber to one task and made sure the view was
updated. Removed myself as a subscriber from one task and made sure
the view was updated again.

Reviewed By: epriestley
Reviewers: epriestley, jungejason, codeblock
CC: aran, rm, epriestley
Differential Revision: 603

src/__phutil_library_map__.php

@@ -277,6 +277,7 @@ phutil_register_library_map(array(
     'ManiphestTaskProject' => 'applications/maniphest/storage/taskproject',
     'ManiphestTaskQuery' => 'applications/maniphest/query',
     'ManiphestTaskStatus' => 'applications/maniphest/constants/status',
+    'ManiphestTaskSubscriber' => 'applications/maniphest/storage/subscriber',
     'ManiphestTaskSummaryView' => 'applications/maniphest/view/tasksummary',
     'ManiphestTransaction' => 'applications/maniphest/storage/transaction',
     'ManiphestTransactionDetailView' => 'applications/maniphest/view/transactiondetail',
@@ -788,6 +789,7 @@ phutil_register_library_map(array(
     'ManiphestTaskPriority' => 'ManiphestConstants',
     'ManiphestTaskProject' => 'ManiphestDAO',
     'ManiphestTaskStatus' => 'ManiphestConstants',
+    'ManiphestTaskSubscriber' => 'ManiphestDAO',
     'ManiphestTaskSummaryView' => 'ManiphestView',
     'ManiphestTransaction' => 'ManiphestDAO',
     'ManiphestTransactionDetailView' => 'ManiphestView',