support OOI, notably auth

[mdutoo]

• 1 support proxying to subpath ('/occi1.1' for ooi) DONE by mdutoo in 6e17787b3cb61095ce7dd8ab80b427d07d03d4b7
• 2.a add hardcoded x-auth-token header in proxy request to OCCI server : https://github.com/occiware/OCCInterface/blob/master/server.js#L17 https://github.com/occiware/OCCInterface/blob/master/server.js#L75
• 2.b fill this token (rather than being hardcoded) in proxyOptions from calls to /conf?x-auth-token=... : https://github.com/occiware/OCCInterface/blob/master/server.js#L47 https://github.com/occiware/OCCInterface/blob/master/server.js#L27
• 3 near the html select & button of the backend URL (top right of the screen), add "auth_header_name" and "auth_header_value" inputs : https://github.com/occiware/OCCInterface/blob/master/src/components/Navbar.js#L116 and read them to fill the call to "/conf" just like and along the backend URL : https://github.com/occiware/OCCInterface/blob/master/src/components/Navbar.js#L53
• 4 if not JSON (trimmed currentJson does not start by '{' or '['), display it without toolification i.e. like 'write' mode (because for now ooi only supports text, though is in the process of completing JSON support): https://github.com/occiware/OCCInterface/blob/master/src/components/CodeView.js#L32

NB.

• "auth_header_name" and "auth_header_value" are not set and dispatched using redux, because it is only used in the HTTP proxy, which is not React.js code.
• later optionally, more headers could be added (such as choosing JSON, XML or text OCCI representation), or a generic way to add any header.