Screen changes update queries

[exerro]

If you give a Screen a width_transition and then update its width, it'll break after calling Application:child_value_changed( Screen ) which in turn calls QueryTracker:update( "child-changed", Screen ) which in turn will test the query function on the Screen which can break if the query is a tag query.

Solution: make Screen extend Sheet and define custom behaviour. They're pretty similar anyway, and then it'll be easier to target them in dynamic values later on. This will allow giving Screens tags and IDs. Nifty, huh?

[exerro]

As Screens don't have an x/y position and are actually pretty different to Sheets, they will simply implement the interface that gives Sheets the tag/ID behaviour. Should fix stuff, if a little hacky.

There may be more problems with referencing Screen values from dynamic values and queries, however.