Fix regression in negative jogs

A bungled rebase on a previous commit caused decX/Y/Z to not have
negative jogs. This fixes that.
Merge pull request #70 from chrisy/feature/jogstep-fix

Fix regression in negative jogs (From Chris)
Translated the 4th axis jog label into French!
- update translation fr
- update Readme (change Grbl84Mega2560 -> Grbl845Mega2560
Add grbl status icons to mainwindow

- added icon showing spindle state
- added coolant icon
- added tool number and feed rate icons
- refactored the incorrect measurement parser
- cosmetic formatting fixes

Add tool number and feed rate icons