Just some code maintenance.

French translation keys added, kindly contributed by Laast

Small rebalance: the steel cost of vents and coolers have been reduced by 5 (cost of 1 wall), to account for the fact that they are no longer walls but rather wall augmentations.

- Support for Gloomy Furniture's walls (as they use a custom thing Class)
- Moved all the hard coded text messages out of the code and into the language keys, in case anyone wants to create some language files.
- Cleanup of some old vestigial code

- Removal of some prototype code related to paste dispensers I accidentally included in the previous release.

- The wall heater's art has been replaced, redone by Ecu.
- Its build menu icon has also been fixed up.

- Update to the patch tie-in for Perspective: Buildings.

- Cleaned up more orphan code which could have been causing some conflicts (Perspective: Buildings used to be part of this mod during its development).

- Cleanup of some unused code.

- Fixes mounted heaters