Remove the StandardPageCache and make Muninn the default
Reduce the memory overhead of the MuninnPageCache

Every instance of a class that overrides the `finalize` method, gets a ~40-byte
companion `java.lang.ref.Finalizer` object, that uses the reference mechanism
to track the lifetime of the object and run the finalizer when needed.

These Finalizer objects also participate in a JVM-wide doubly-linked list,
which worsens the GC pause times.

These issues have been fixed by introducing a MemoryReleaser that knows about
all the raw pointers that we will want to release, and then every MuninnPage
has a reference to the MemoryReleaser. When all the pages have been collected,
the MemoryReleaser becomes elegible for finalization, and then it will free
all our pointers in bulk in its finalizer method.
Make community tests pass with the MuninnPageCache

... without running out of memory
Merge pull request #3086 from chrisvest/2.2-muninn-ftw

2.2 Make Muninn the One True PageCache
Evict from cache as late as possible in race test.
Exact number of relationships given node label.

The CountsStore maintains the exact number of relationships in the
database that either starts or ends in a node with a given label. Counts
are maintained both in total, and by relationship type, but only for one
label, i.e. number of relationships that starts in a node with a given
label and ends in a node with a given label is not maintained.