Concept Insights: fix corpus id in createCorpus

[msushkov]

Concept Insights API requires corpus id to be of the form /corpora/{account_id}/{corpus}. createCorpus() takes in a Corpus object, where an id is required. createCorpus() creates a URL for the request by concatenating /v2/corpora/{account_id} and the id from the Corpus object; currently this concatenation results in /v2/corpora/{account_id}/corpora/{account_id}/corpus.

Proposed solution: since Concept Insights API does not require an id for the corpus, allow Corpus.id to be null in createCorpus(). Add a name field to Corpus and use that when calling createCorpusIdPath() from createCorpus().

[msushkov]

@alseddnm

[germanattanasio]

@alseddnm is working on this.

[germanattanasio]

@alseddnm did some work on this e447b8c

[germanattanasio]

fixed in the next release