Updated key retrieval for elsevier client
Updated key retrieval for elsevier client

Now tries elsevier key file for both api and institution keys, and if
there is a problem reading the files, looks in two environment
variables.

sorgerlab/indra,bgyori/indra,johnbachman/indra,johnbachman/belpy,sorgerlab/belpy,johnbachman/belpy,jmuhlich/indra,pvtodorov/indra,pvtodorov/indra,johnbachman/indra,johnbachman/indra,bgyori/indra,pvtodorov/indra,pvtodorov/indra,sorgerlab/indra,jmuhlich/indra,sorgerlab/belpy,jmuhlich/indra,bgyori/indra,sorgerlab/indra,sorgerlab/belpy,johnbachman/belpy