This involved adding a list to the DisasmProject, creating a new
UndoableChange type, and writing the project file serialization
code. While doing the latter I realized that the new Width field
was redundant with the FormatDescriptor Length field, and removed it.
I added a placeholder line type, but we're not yet showing the
table in the display list. (To edit the tables you just have to
know where they are.)
The table editor is now editing the table, and the DefSymbol editor
now asks for the Width data when editing a local var.
This also moves EditDefSymbol closer to proper WPF style, with
bound properties for the input fields.
No changes yet to serialization or analysis.
