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