Add switch to store GWT mode

In hosted mode, GWT can produce helpful debug info in the log. In
production mode, GWT can only use JS $wnd alerts. This switch allows me
to write code to run in either mode for debugging.
Add overloaded ModelTree#isComponentPresent

As a convenience, add an overloaded version that takes a component id
as input. The original #isComponentPresent calls this method.
Fix bug in clearing ParameterTable

When a Component is deleted from the ModelTree, check beneath it in the
tree for a Component that has parameters on display in the
ParameterTable. If found, clear the table.
Fix issue with separator lines persisting after clearing ParameterTable

Just clobber all the rows, since the table gets rebuilt for each
component's parameters.
Progress on deserializing model

I can open a model and display its driver in WMT. Now I need to think
about how to handle what comes next.