Fix for #1104: only log missing type errors if we use them, as determined by a new visitor

This way we can avoid most missing type errors as long as we don't use the offending methods/types
model loader: #1104: do not log missing type errors anymore, but store them in the UnknownType

So they can be reported only if actually used
Added test for #1104
updated tests for #1100: we generate a lot less errors now :)
Updated error message for #1180 now the typechecker fixed it
Ignore failing test for #1195 now the typechecker added an error