www/py-websocket-client: Update to 0.56.0

• Update LICENSE [1]
• Update pkg-descr, add WWW: URL
• Add USE_PYTHON=concurrent, package installs a script
• Remove backports.ssl_match_hostname dependency, only needed for Python < 2.7.9 [2]

Changelog:

https://github.com/websocket-client/websocket-client/blob/v0.56.0/ChangeLog

[1] https://github.com/websocket-client/websocket-client/commit/e94ed9e078c7772a7dc0a115da1a34c493f290b6
[2] https://github.com/websocket-client/websocket-client/commit/f7f5f70681c621d169b82fc842cb2396265203d5

Reviewed by: alfred (maintainer)
Approved by: alfred (maintainer)
Differential Revision: D20283