Allow a Sud step to combine a ramp and a hold

A step can now carry both 'ramp' and 'hold': it ramps to the target
temp, then holds there for the given duration, instead of needing two
separate schedule entries. Sud.temp_reached() switches such a step
from its ramp phase into its hold phase in place (re-firing the
step-changed callback so SudTask/demo_sud re-apply the hold's stirrer
settings); user_wait_for_continue still applies once the whole step -
both phases - is done.

Merges sud_0010.json's three ramp/hold pairs into combined steps.

client/brewpi_gui.py

@@ -130,7 +130,8 @@ class SudForecastPlot(FigureCanvasQTAgg):
 	def _estimate_course(schedule, start_theta):
 		"""Walks the schedule, accumulating (t, theta) waypoints: ramps take
 		abs(delta)/rate minutes at the declared rate, holds last for their
-		duration at the temperature the preceding ramp reached."""
+		duration at the temperature the preceding ramp reached. A step may
+		carry both - ramp then hold - contributing both segments in turn."""
 		t = [0.0]
 		theta = [start_theta]
 		for step in schedule:
@@ -142,7 +143,7 @@ class SudForecastPlot(FigureCanvasQTAgg):
 				if rate > 0:
 					t.append(t[-1] + abs(target - theta[-1]) / rate * 60.0)
 					theta.append(target)
-			elif hold is not None:
+			if hold is not None:
 				t.append(t[-1] + hold.get('duration', 0) * 60.0)
 				theta.append(theta[-1])
 		return t, theta