Create a UI for password changes

[thomas-schroderadveq]

Is your feature request related to a problem? Please describe.
For users without a Gmail account: it would be nice to be provided with a username and dummy password that can then be modified by the user, so that privacy is preserved.

Describe the solution you'd like
Create a UI that allows the user to modify his/her password after the first login.

[leupibr]

@thomas-schroderadveq currently there's no possibility to self-register without a Google account. I'll create a ticket for that too. Further I will also create a ticket for SSO/Signup with a Github account which could be a real alternative to Google.

The password UI should only be a last resort, as the SSO feature of the big providers are much more secure than a custom implementation. However, it could be a use case under certain circumstances and I'll include it into the next release.

[leupibr]

See #31 and #32 for up vote and/or subscription.