Code Review Changes

[doulikecookiedough]

Optimizations to be made after reviewing with Jing (HashStore-java)

Part 1: Refactor find_object to throw relevant exceptions for the following scenarios:

• pid refs file exists but the cid that it is referencing does not have a cid refs file / does not exist
• pid refs file exists, cid refs file exists but the expect pid is not found in the cid refs file

Part 2: Update delete_object

• Refactor delete_object to handle customized exceptions above
• Re-arrange order of deletion - pid refs file should be removed first

Part 3: Change ObjectMetadata's id attribute to be 'cid' to be explicit about what it represents

• And fix affected code

Part 4: Update verify_object return value

• Should return a boolean, and should not delete the files associated with the supplied ObjectMetadata (if it does)
• Fix affected code

Part 5: Add new overload method for delete_object

• When storing only data, if the data turns out to be invalid (because of a mismatched size or checksum), we need a method to delete the data only.
• This will be implemented in another feature branch with additional changes to delete_object

Part 6: Do not throw exceptions when calling delete_sysmeta on a metadata document that does not exist.

Part 7: Confirm that an exception is not thrown when called storing an object that already exists

[doulikecookiedough]

These items along with Matthew's feedback have been made and merged into develop via Feature-85: Code Review Optimizations