Hide tabs that aren't relevant

[bmaranville]

Currently, every panel that is defined in the webview application is shown in the tab chooser all the time. This includes the 4 uncertainty plot panels, that really only should be shown when there is an uncertainty state defined in the server state. It also includes the new Custom Plot panels, which should only be shown if the models define any custom plots.

Implementation:
Could add logic to panels to decide if they should be shown or not, depending on the shared state in the client. Need to add "uncertainty available" to the shared state, as well as "custom plots available".