Post update to companies

Adds functionality to create "Shares" for companies.  See https://developer.linkedin.com/creating-company-shares.  It also includes the ability to target company Shares (see https://developer.linkedin.com/documents/targeting-company-shares).  This last part, however, is broken on the LinkedIn side when exchanging JSON payloads (see https://developer.linkedin.com/forum/targeting-example-using-multiple-targeting-parameters-and-json) so I had to revert to using XML instead.  This introduces the use of XStream and adds extra logic to error handlers and interceptors.   This can be "sanitized" once LinkedIn fixes their API.