1) custom HS/IS urls are now persisted in HTML5 local storage. As a result, all the login components now distinguish between default HS/IS URLs and custom specified ones again. (
2) custom HS/IS urls are synchronised between the instances of ServerConfig found in the Login, Registration and Forgot Password screens.
3) username are persisted over changing homeserver (but not password, to stop accidentally leaking passwords to the wrong server)
4) correctly interpret a blank URL field as meaning the placeholder text
5) when toggling custom URLs on and off, remember what the custom values were, and use the default URLs if custom mode is not engaged
also, guest access now upholds custom HS/IS URLs found in local storage rather than being limited to the server config ()
also adds assorted comments and improved console debug and a few minor cosmetic changes to the login components.
this commit sponsored by VS27...
Instead of using the Room's active timeline directly, use a
TimelineWindow. This shouldn't (yet) have much effect, beyond maybe making
scrollback after a gappy sync slightly more efficient.
For now, I have disabled the 'restoreScrollState' functionality. This will be
reinstated once I land the link-to-event code.
