Dereference external members

[hdelva]

Changes:

• Updated the Comunica dependencies, which fixes the TREE metadata extraction
• Building the member objects from a stream of quads stops when it encounters another member, or when a cycle is detected
• External members can now be dereferenced
• Added rate limiting, because dereferencing members can cause some issues
• Cleaned up the error handling, so that failed to process one member doesn't skip the whole page