I was unsure how to update the QwtPlotPrintFilter code, so I just commented it out with a FIXME.

Also deleted invalid line drawing options.

Fix HIL link reconnect issues due to missing threading flag usage, warn user about missing config and take him to config view if necessary

espeak: provide string length with 0 character, fixes problems with qgc reading out strange values/chars at the end of the sentence

This way the delete happens on the right thread.

Current version was not as clear as it could be.

Most math and backend storage was floats anyways, so most of these changes just half the data copied during function calls without reducing precision.

Otherwise MANUAL_CONTROL messages are still sent at the regular 50Hz. This reduces transmission bandwidth from 0.9kbps when the joystick is used continuously to 0.1kbps when it's idle.
To prevent possible issues from the last high-bandwidth message being lost and the system then not responding for .1s, the last messsage is double-transmit which should prevent those issues.