Filesystem for CM_File

Some new code, paired with Chris, todo:
- [x] add file read cache (see bf43f99d5eb8409af5042e6d1ddbfc5eb4c909f3 + invalidation on delete and other operations?)
- [x] clean up file test (moved code to local FS test)
- [x] Replace code in CM_Util with calls to filesystem
- [ ] Separate filesystem service for temp userfiles (s3 bucket without versioning?)
- [ ] stream for local filesystem (uploading big files to s3?)