Object Listing

Support the list objects functionality of s3. Bucket only GET requests
get a response with a list of the objects in the bucket

Change log:
* add list object functions to the phobos_cpp_wrapper
* add listing objects to storage functionality
* add bucket object listing wrapper to stream
* empty list objects function is disk storage backend to satisfy storage class
* string_to_map function to aid returning object_list in storage
* remove Catch2 header file
* oid_to_key function to parse away bucket from object name
* s3_utilities: function to create xml response for list objects
* bucket only GET request calls list objects
* get_request_handler: respond with object_list for bucket only requests
* add object listing to unit tests
* integration test for object listing
* unit test for empty bucket
* integration test for empty bucket
* Use bucket and key in unit tests to reflect actual usage
* generate random bucket name for testing so number of objects in
    returned list can be measured
* replace assertTrue with assertEqual in integration tests where appropriate
* number integration tests to ensure order (alphanumerical) of execution
* instruct integration tests to stop on first error
* free object meta data struct
* fix development flags not being used during debug build
* use debug build for CI
* use release build for CentOS7
* appease development flags
* disable LeakSanitization for CI (does not work on Gitlab-CI)
* source relevant env list in CI before_script
* export LD_LIBRARY_PATH in CI configure step
* pass bucket name to xml parser to avoid attempting to access an object of an empty list
* update documentation
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