[Pianod] New query string parameters for client

[Perette Barella]

A couple new options for the ‘login’ query parameter:
* login=login : Logs in only if there are stored credentials.
* login=visitor : Logs in as a visitor without clobbering existing credentials.  A new button on the login pane provides similar interactive functionality.
* login={username} : If stored credentials are that user, automatically logs in.  If they are unset, fills in the suggested name.  If they are set but don’t match, shows the login window.

Also:
size=fixed : Disables the pane-width responsiveness.  Number of panes is still responsive.

Changes are currently in test here:
	http://draft.deviousfish.com/Df/pianod/client/index.html
and will be promoted in a few days.

Perette