This is the first of several large commits changing several aspects of
the handling of defaults. The overall main purpose of these changes is
to protect against using non sensible values in the case the values have
not been sensibly specified in the deck. The changes in this commit
include:
1. The "default default" values to be used when an item without an
explicit default are defaulted are removed completely.
2. If a ParserItem is queried for a default value when no default has
been assigned it will raise an exception.
The purpose of this flag is to keep track of whether a keyword is
supposed to have only one element, i.e. scalar, or several. The
defaultApplied method only makes sense in the case of scalar items, this
method will now throw if it is called on a non-scalar item.
