made signals.BasicVariable.diff conistent with quantity.Discrete.diff and some further beautifications

unittests.quantity.testSymbolic: testSolveOde is like a zombie and comes back again and again... deleted it again.
unittests.misc.ss.testSs: removed one 'domain' which was part of name-value-pair domain input.
-> all unittests work without errors!

- unittests for quantity.Domain/Discrete and /Symbolic
- deleted unittests.quantity.testSymbolic/testSolveOde

     unittests.quantity.testBasicVariable/testBasicVariableInit    X         X       Errored.
     unittests.signals.signalsTest/testGevreyBump                  X         X       Errored.

- new method remove()
- rename: renamed "copyAndRename"-method into "rename" and rewrote it

The simulation for fractional systems returns now the distributed system variable as quantity.

This reverts commit b66c5afa.

-> unittest for testDiscrete are working

it was not covered by a unittest, so I added one

# Conflicts:
#	+quantity/Discrete.m