add a new checkbox to the yasgui settings, allow using password protected endpoint

[SimonBin]

Some endpoints are protected with basic auth

see

• https://github.com/Triply-Dev/YASGUI.YASQE-deprecated/issues/94
• https://github.com/TriplyDB/Yasgui/issues/45

I have tested the code with our public and password protected fuseki

you can enable the "login" request in the cogwheel settings, thus it does not break any normal non-protected endpoints. When enabled, the withCredentials flag is turned on and iff the endpoint does require authentication, the user is prompted by their browser to fill in the HTTP basic auth credentials. The browser caches this login for the rest of the session

if you on the other hand enable the checkbox on a public endpoint, then you get the "Unable to get response from endpoint. Possible reasons" error (as expected)