all: fix VleUtils scripts and fix vle.forrester

- definition prefix in VleCheckPackage did not take into account the
possibility to have module version into package dependencies.
- vle.forrester was not linked to ext.muparser
README: update
switch to VLE 1.3
Add a build script
switch to gtkmm3:

- all: update CMakeList.txt and FindGVLE.cmake files
- switch to gtkmm3 for vle.output
- switch to gtkmm3 for vle.extension.difference-equation
switch to gtkmm3, continue:

- switch to gtkmm3 for vle.extension.decision
- switch to gtkmm3 for vle.extension.fsa
- switch to gtkmm3 for vle.extension.petrinet
- switch to gtkmm3 for vle.extension.forrester
- fixes for vle.extension.difference-equation gtkmm3 version