Fix routing of posts and static pages

closes #1757 and #1773

- switches routes.frontend for posts and pages
to use a regex with two capturing groups.  This removes
the need to dynamically remove an express route at a
later point, leaving the decision making to frontend
controller.

- added unit tests for all routing conditions that 
can arise for posts and pages.

- updated functional tests to also test for same thing
in unit tests

- removes old code from server/api/index that used
to fix this issue, but is no longer needed

- removed some un-needed require statements in routes/admin