Fan speed will be ramped up linearly from zero at layer disable_fan_first_layers
to maximum at layer full_fan_speed_layer. full_fan_speed_layer will be
ignored if lower than disable_fan_first_layers, in which case
the fan will be running at maximum allowed speed at layer
disable_fan_first_layers + 1.;
WIP: The cooling PresetHints are likely not finalized yet.
This can happen if the user enters invalid toolchange through the custom gcodes
Such toolchange is now simply ignored by the CoolingBuffer, exporting gcode is NOT stopped, a log error is emitted
from the current Model/ModelObjects.
Fixed a possible race condition in updating Print::m_placeholder_parser
with the proposed filename / filename base.
Improved documentation (source code comments).
