The backend selecting mechanism needs all modules to be imported.
This commit restructures the package to be able to do that. Placement
of some functions felt weird, but this can still be changed.
No more placements in __init__.py anymore though, as this will
result in cyclic dependencies.

Some work on parameter classes, a bugfix on the splitting algorithm
some simplifications in the generation stage

as a consequence introduce template parameters

to dependency extraction
lfs generators
geometry stuff

The cache_context functionality helps greatly here.