Made SRX/SRJ parsing deferable, with the aim of passing straight through
if possible.
Major refactor of parsing and serializing. SPARQL queries work, but lots
of other stuff probably doesn't.
preferred_media_types now on Endpoint constructor on all StoreViews
Added priority to srj so srx is preferred when all is otherwise equal.
Removed unused code.
Tidying up SPARQL views.
Got CannedQueryView working again.
rdflib parsers can now have args/kwargs passed through.
StreamingParser.get() now binds namespaces for graph results.
StreamingParser.format_type added to tell between graph and SR parsers.
Tidied whitespace.
Removed unused imports
Fixed ==/= mix-up
RDFlib parsers can only be called once.
Endpoint now pushes up faster formats if an unsupported format is
requested.

Unsupported formats will require transforming, and therefore parsing. If
we're parsing, we should pick a format we can parse most quickly.
Endpoint.query() now takes defer arg, to mimic previous behaviour.
archive task now uses new streaming API.
Fixed GraphListView (CannedQueryView before HTMLView in mro)
Moved undefer from CannedQueryView to StoreView.
Added functions for finding parsers/serializers by extension.