test(pageservice): add tests for page service

[seaerchin]

Problem

previously, PageService had no associated tests; this PR add the tests in.

Solution

1. write unit tests for pageService
   • the unit tests are centered around parsePageName together with retrieveStagingPermalink; the invariants that we want to guarantee will be briefly outlined below
   • for static pages (pages whose name are always fixed), maintain the invariant that only that specified filepath can be parsed into that name
   • guarantee that for resource rooms, we will only get permalink for posts
   • recursive descent (ie, the order in which we attempt to parse is fixed)
   • note that filepaths terminating in / will not have a name property - consistent w/ how directories behave; we could extend our model to also parse directories but this is not done at present. this should also not be possible if we are receiving from the fe

[dcshzj]

Briefly looked through the test cases, seems ok to me.

[dcshzj]

I think this concerns mainly the original PR, but should we change this to use an enum instead?

[seaerchin]

actually i ran into troubles with using enums as types in the past and hence, i didn't use it here. i think the original PR has a comment about this raised by kishore also