Use URLEncoder#encode with the encoding specified.

We should set the name of character encoding to UTF-8 explicitly
because URLEncoder#encode without the encoding parameter is deprecated
and the W3C states that UTF-8 should be used according to Java API docs.
Use decode with the encoding specified.
Merge remote-tracking branch 'upstream/master' into avoid-deprecated-encode
Replace another URLDecoder#decode.
update changelog with closed JIRAs