Simplify expressions

Simplification of expressions (important only if critical bottlenecks are found):
    - Improved simplification of Indexed/ComponentTensor combinations.

    - Implement better simplification as an algorithm, or add
      more simplification features to __new__ implementations?
      One important such basic simplification is to extract constant
      factors from all operands in a sum, e.g. from:
              (-1 * (v_1)[0])
              +
              (
              (2 * (v_1)[0])
              +
              (-1 * (v_1)[0])
      to:
              (-1+2-1) * (v_1)[0]) = 0
      Once form compilers and regression tests are up and running,
      we can consider wether the backside of this (which is complicated)
      is important enough to avoid doing this by default...
      IT IS VERY IMPORTANT TO HAVE A GOOD AND __COMPLICATED__
      SET OF TESTS IN PLACE BEFORE DOING THIS!