Support limiting maniphest queries to specific ids

Summary:
This limits a maniphest task query to only contain certain ids set
by the tasks query parameter.

Test Plan:
none yet, i wrote this at a computer with no phabricator
install while bored and eating dinner.

Reviewers: skrul, epriestley

Reviewed By: epriestley

CC: aran, davidreuss, epriestley, skrul

Differential Revision: 1137