Flask demo client-side js

[gradyy]

getCredentialCreateOptionsFromServer and getCredentialRequestOptionsFromServer differ only by a hardcoded url. The same applies to postAssertionToServer and postNewAssertionToServer. These functions can be consolidated into functions that takes the url as a parameter.

This change is to improve readability. The destination urls have been moved to the main body of didClickRegister and didClickLogin to help the reader more easily identify the server-side function being invoked at each step of the registration or authentication process. In short, the information is all in one place. Having less code to review should also be a plus for the readability factor.

A future improvement may be to use Flask templating and url_for to insert the appropriate urls at runtime.

commits prior to da4a230 are duplicated from #67

[gradyy]

one commit duplicated from #73 removed unused copy of JQuery.

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