Solves issue with SendWorker failing because it cannot start a Thread when constructing a connection pool. This solution is to do away with the connection pool. Since we are only ever using the ConnectionManager with a single thread (which is then discarded) there is no problem with multi threaded interference.
Merge pull request #165 from william-ferguson-au/issue-136

Solves issue-136 - SendWorker failing because it cannot start a Thread on App destruction