Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE-99

- Bug Fix: Block Controller has the same content-type bug
- Bug Fix: When assigning content-type to 'application/binary' we need to set the content-length
- Enhancement: Added a method to get the length of a file/block from the Vault Model
- Enhancement: Added a method to get the length of an object from the storage drivers
- Enhancement: Added a method to get the length of a file from the metadata drivers
- Enhancement: (Cassandra) Added a text 'size' field to the files documents
- Enhancement: (Sqlite) Added an integer 'size' field to the files table
- Enhancement: (MongoDB) Added size field to the files documents
- Enhancement: Updated the Swift Mocking to return the "required" headers when getting an object
- Caveat: MongoDB driver is not reporting the file size correctly for some reason (test_sqlite_driver.py: line 261, returns 0)
- Caveat: Swift Driver is having issues with deleting the vault in the tests (test_disk_storage_driiver.py: line 125)
- Caveat: There are still some coverage issues