(Hopefully) Fixed several bugs with respect to the coordinate system used.
There was a bug reported by Sven Möller that caused _action_of_Gamma0 to fail
because this method still used the old ._L list of elements in WeilModuleElement.
However, there werde quite a few bugs regarding the use of the el_index etc. - methods.
This is all due to the fact that can_coords=True has to be used
when the generators and their orders are used for the coordinate functions.
I think this should be changed to using the elementary divisors instead.
But for now, I just fixed the bugs (ugly...)

Conflicts:
	psage/modules/weil_module.py
Merge remote-tracking branch 'stephan/weil_module_bugfixing'
Added some documentation and fixed random_element and the test_formula function
Added a reimplementation of an_element() since the default function used multiplicative instead of additive group