Add SameSite flag to work with Firefox Nightly

[earthengine]

A quick fix for #2544.

Tested in my own computer with doing the same to the UiPasswordPlugin.py file.

[earthengine]

This is not working yet. It fixed in Firefox Nightly but breaks Chrome.

The test result is: if we set "SameSite=None" only, it works in Chrome. But in Firefox Nightly it stops the user from logging in (keep showing the login page). On the other hand, if we set "SameSite=None;secure", Firefox Nightly likes it but Chrome (and Edge) keep showing the login page.

I don't know what the correct solution should be; but I think ZeroNet will have to implement HTTPS and so "SameSite=None;secure" will work on both if using HTTPS.