the Transform class does not allow to specify arbitrary wavelets

As discussed in https://groups.google.com/forum/#!topic/bob-devel/y6PVFkD_V68 the Transform class cannot use an arbitrary selection of wavelets, but always fills with a grid of wavelets. It would be great to have the possibility to pass an [Wavelet] to the constructor, too.

This would include to go over all the code and see, where the wavelets are actually used. I guess, it will also need a change in the I/O, i.e., to write and read the set of wavelets when they are set by hand.