No timeout on material change procedure

[ghost]

When changing material, it can happen that after removing the material, the user leaves the machine in the 'Remove material' state. During this time the hotend is heated, and this state currently persists until the machine is switched off or until a user intervenes.

This means remaining polymer in the printhead degrades and carbonises, leading to clogged nozzles.
The effect on the teflon isolator is yet unclear.

Suggestion is to implement a timeout that aborts the procedure and cools down the nozzle if a material is not inserted in a certain time window ( for example 10 min ).