Add memo to file entity type

[tinker-michaelj]

Related issue(s):

• Closes Add memo field for file entity #962

Summary of the change:

• Add memo field to JFileInfo -> HFileMeta type, update serdes version.
• Add memo syntax checks in file create/update transition logics.
• Respect memo in create/update transition logic.
• Incorporate memo size in fee calculations, refactoring to follow the new estimate pattern.

External impacts:
Will cause a very small increase in fees charged for some FileCreate and FileUpdate operations.