Taught bitcoind to close the HTTP connection after it gets a 'stop' command,
to make it easier for the regression tests to cleanly stop.
Move bitcoinrpc files to correct location.
Tidied up the python-based regression tests.
- Add license headers to source files (years based on commit dates)
in `src/test` as well as `qa`
- Add `README.md` to `src/test/data` specifying MIT license
Fixes#3848
