escaped micro symbol breaks graphDB

[joshmoore]

          A heads up that this apparently is failing for graphDB on the micro symbol

_:N601882e7d0f24751893771b77ef8b624     http://www.openmicroscopy.org/rdf/2016-06/ome_core/Symbol     "\xb5m"

Originally posted by @joshmoore in #24 (comment)

[joshmoore]

Other graphDB parsing issues:

cc: @andrawaag

[joshmoore]

@andrawaag: my new-context branch (#30) fixes this issue but significantly changes the output URIs. See e14258b .