`make share/slangscripts.sl' creates a collection of functions that only rely...

`make share/slangscripts.sl' creates a collection of functions that only rely on S-Lang, but not on ISIS

Changes:
- `gridmapping' does not support the plot qualifier anymore, but runs much faster now
  ("A function should only do one thing and do it well...")
- Likewise, `inversemapping' does not plot its (intermediate) results anymore