Update Qwt to 6.1

Fix linux release build warning

Plotting data now defaults to drawing a line with no symbols.

Qt5 fixes

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

We also document how we got the source code and keep our modifications out of the Qwt directory.

Also deleted invalid line drawing options.

espeak: provide string length including 0 character

Removed mavlinkgen application.

Refactor MAVLink packet loss calculations

Detach the map widget - rebase

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

Reduce the transmission rate of MANUAL_CONTROL messages when command inputs have not changed

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.