Rename: UserID -> NymID.

Addendum to 05d50e5.
find . | egrep "(cpp|hpp|proto)$" | xargs sed -i -e 's/UserI[dD]/NymID/g'
Rename message/API: issueInstrumentDefinition -> registerInstrumentDefinition.

Addendum to c43a1a7.
find . | egrep "(cpp|hpp|proto)$" | xargs sed -i -e 's/issueInstrumentDefinition/registerInstrumentDefinition/g'
find . | egrep "(cpp|hpp|proto)$" | xargs sed -i -e 's/IssueInstrumentDefinition/RegisterInstrumentDefinition/g'
Merge pull request #458 from benma/renamings

Rename: UserID -> NymID, issueInstrumentDefinition -> registerInstrumentDefinition