EasyRdf unable to guess format

[jimsafley]

See https://forum.omeka.org/t/vocabularies-ontology/7200

BBC publishes its ontology in Turtle format (ttl). For some reason EasyRdf cannot guess the format, so it raises an "Unable to parse data of an unknown format" exception. After I explicitly set the format to "ttl" in the controller, the vocabulary successfully imported.

We could instruct the user to convert from Turtle to another format, such as N-Triples or RDF/XML, but we should probably just allow users to select the format on the import form, defaulting to "guess".

BBC Ontology: https://www.bbc.co.uk/ontologies/bbc
Download RDF: https://www.bbc.co.uk/ontologies/bbc/1.10.ttl

[zerocrates]

Looks basically like EasyRdf will only "detect" Turtle if it sees @prefix or @base in the beginning-ish of the file.