Minor firmware release 1.17b

dc42

Firmware 1.17b is now live on github at https://github.com/dc42/RepRapFirmware/tree/dev/Release/Duet-WiFi/Stable (remember to follow the link on that page to 1.17b and then press Raw to download it). Changes:

New printer status "Tool change" implemented. This is recognised by DWC 1.14 and the forthcoming PanelDue firmware 1.16.
Bug fix: M226 (gcode-initiated pause) was hanging the printer (thanks chrishamm for the fix)
For Z probe types 4 and higher, the MOD signal on the Z probe connector is driven high at the start of a probing move and low at the end. This is to help with certain types of Z probe, in particular accelerometer-based Z probes.
Upgraded the associated DWC files to 1.14 release (thanks chrishamm)