If the requested object in states.json exists but doesn't contain the
property we're looking for, return the default value (passed to the
function) instead of undefined.
Use native ListModel which require a lot of changes, but should be
much faster than the old way which exponentially slowed down to a crawl.
Also fix some popup bugs (leave/forget).
Not working yet: side pane keyboard controls, proper highlight,
room & member filtering, local echo replacement
