Allow configuration for whether a job calls tech support upon failure

[alarthast]

From this comment: #634 (review)

Currently the line to call tech support upon a job failure is already nested in an if statement.

bennettbot/bennettbot/dispatcher.py

Lines 151 to 152 in ee648c1

	if not self.job["is_im"]:
	msg += "\nCalling tech-support."

It should be fairly straightforward to add a second condition to that if statement that is dependent on a boolean property captured in the job config.