Support remove methods for SynBioHub Collection and Parts

[tramyn]

SynBioHub has a backend remove support for deleting a specified Collection and a specified part base on the given URI.
This functionality is not supported in libSBOL. It would be great to have this feature supported in the libSBOL library.
Refer to the SynBioHub issue that was reported here for more information on how to call the remove method in the backend of SynBioHub.