Write a general Add-Method

[sebastianpos]

The Add-Methods need some enhancements:

• write them more general, i.e., only distinguish the general cases described in the manual
• allow lists of functions which cover all possible cases as an input
• give the weight of a function as an (optional) parameter

[sebasguts]

The default value for the weight should be high, at least higher than the longest chain of derivations one would expect.

Also, there should be some testing method which can make good guesses of the weights for the primites.

[sebasguts]

Add-Methods are now (up to some special cases) installed automatically (694e8c2). Special cases are marked by the no_install flag in the method record. Stuff left to do by now:

• Look at the special cases, install the hook for AddPrimitive and make them compatible to the new list structure.
• Delete the other adds
• Add derived methods to the graph, also look if they are okay.
• Change the derivation view method to use the graph.