Enable admin to view and delete other users' herald rules

Summary:
enable admin to delete user's herald rules. This is useful for
managing non-active users' rules. For example, ex-employees' rules. The
code change includes:

• Added a 'All' tab which is only accessible to admin.
• Refactor out a HeraldRuleListView which is used by both the home controller and the all rule controller

Test Plan:
delete an ex-employee rule as an admin; disable myself as
admin and verified that I don't have access to view other user's rules
and I'am not be able to delete them; also verified that as a non-admin,
I can still view, create and delete my own rules.

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: aran, epriestley, jungejason

Differential Revision: 1064