When a test module was selected using the gui, the absolute path
to the file was saved. At execution, the local directory prefix "."
was prepended, which led to wrong paths like "./home/bjp/testModule.curry".

The old implementation had some flaws:

  - The type signature of a function was not taken into account during
    inference, leading in a type divergence of the function and its body.

  - Because of missing annotations, rules, rule variables and
    patten variables could not be typed,
    leading to a more complicated structure.

  - Identifier (type `QName`) now also get a type annotation in patterns
    and function/constructor calls. This allows the annotation with a
    fresh variant of their type during the annotation phase and removes
    the necessity to lookup their types during inference.

  - The `ErrorState` and substituion functionality are now extracted into
    seperate modules to allow re-usage.

Although the type inference takes into account the type signature of
functions during inference, the resulting declarations got the inferred
type of the function rule, which could be more general.

The new implementation now checks whether the type provided by the
function signature is an instance of the inferred type and keeps it.

The original implementation required the imported modules to be available
using the curry system's load path. Two new functions now also allow
passing a local environment, mapping module names to FlatCurry programs,
to be passed alternatively. In consequence, no IO is necessary.