Improve error messages, which mention module parameters.

[yav]

Fixes #1560. There are two main improvements:

• When printing module parameters from anonymous module interfaces (i.e., parameter) don't show the module name.
  So, instead of saying M::M__parameter::x we just say M::x.
• When referring to module parameters in error message just use the variable name (e.g., x instead of M::x).
  • To avoid name conflicts we add suffixes (e.g., x₁)
  • After the error we add an explanation linking the names used to the actual parameter (e.g., where `x` is module parameter `M::x` )
• When printing quantifiers in error messages, we only print variables that are actually mentioned in the error.

[RyanGlScott]

Hooray! I'm quite happy with how the error messages look now.

LGTM, aside from some minor suggestions.