Move RepeatRule to the io test package

Also not a todo comment on an important area of the page cache that needs more testing.
Also extract some threading utilities out of the PageCacheTest into a utility class.
Fix a page cache bug when faulting throws

Both the StandardPageCache and the MuninnPageCache had a bug where, if IO on swapping a
page in threw an exception, the page faulting procedure did not properly clean up after
itself.
This left the page caches in inconsistent states, that would eventually lead to
deadlocks.
Make the MuninnPageCacheTests run faster

... by not doing explicit GC when the page cache is closed.
We disable this feature anyway on all platforms but Windows.
Fix js error when expanding graf.

Set placeholder value for relationship captions.
Merge pull request #3024 from chrisvest/2.2-flaky-pc-test

Fix a page cache bug when faulting throws
Get exact count of number of nodes in the graph.
Get exact count of number of nodes with given label.
Get exact count of number of relationships in the graph.
Remove unused statistics service.