BAG_EVERY added to bagSyntax

Some more additions to bagLib. I'm mainly interested in bags that consists of multiple insertions into the empty bag like for example {|x1;x2;x3|}.
I call these explicitly given, finite bags "simple".

There was a lot of tool support for handling bags that consists of BAG_UNION applications. One can eliminate those for example on both sides of an equation, a BAG_DIFF ...
Now I added support for these "simple" bags. I started adding some things like resorting to bagLib before. However, these addidtion became larger and larger. Therefore, I moved them
into an new file called bagSimpleLib. However, it is imported by bagLib, so the end-user does not need to know this.

BAG_IMAGE_CONV added that is able to evaluate BAG_IMAGE on very simple bags. Moreover, some extensions to bagSyntax were made.

Added BAG_RESORT_CONV. This new conversion is able to sort nested uses of BAG_INSERT. For example
BAG_RESORT_CONV [0,3,2] ``{|x0; x1; x2; x3; x4|}`` results in {|x0; x3; x2; x1; x4|}

Changed a couple of misleading/annoying names. The type ssdata is now
called ssfrag (to bring it into line with documentation that talks about
simpset fragments), and the constructor SIMPSET is now called SSFRAG.
It never created a simpset, so the latter was a stupid name.

Slight re-org.

Builds in Kan.0.

CANCEL_CONV can loop where both arguments to the binary function are
the empty bag. This can't be allowed in a simpset, so the actual conv
used in BAG_ss is now CHANGED_CONV CANCEL_CONV.

Extended bag library. Decision procedure for solving sub-bag or
equality goals has been added. The CANCEL_CONV conversion has also
been extended to do its thing over BAG_DIFF terms. It has been put
into BAG_ss. If it proves to be too inefficient there, I can always
take it back out.

Implemented a bag library, to help with standard tasks, and provide at
least one useful tool (CANCEL_CONV).