It's not quite the same as the character encoding -- sometimes we
want a mix of things -- so it gets its own enum. The value is
saved to the project file, but not actually used yet.
Also, moved some combo box strings into XAML resources.
SourceGen creates "auto" labels when it finds a reference to an
address that doesn't have a label associated with it. The label for
address $1234 would be "L1234". This change allows the project to
specify alternative label naming conventions, annotating them with
information from the cross-reference data. For example, a subroutine
entry point (i.e. the target of a JSR) would be "S_1234". (The
underscore was added to avoid confusion when an annotation letter
is the same as a hex digit.)
Also, tweaked the way the preferred clipboard line format is stored
in the settings file (was an integer, now an enumeration string).
