Reorganized memory blackboxing (#336)

* Reorganized memory blackboxing

Moved to new package memlib
Added comments
Moved utility functions around
Removed unused AnnotateValidMemConfigs.scala

* Fixed tests to pass

* Use DefAnnotatedMemory instead of AppendableInfo

* Broke passes up into simpler passes

AnnotateMemMacros ->
  (ToMemIR, ResolveMaskGranularity)
UpdateDuplicateMemMacros ->
  (RenameAnnotatedMemoryPorts, ResolveMemoryReference)

* Fixed to make tests run

* Minor changes from code review

* Removed vim comments and renamed ReplSeqMem