linux speech synthesis: switch to eSpeak

Conflicts:
	QGCExternalLibs.pri
	src/GAudioOutput.cc
Added 2 kPA offset to pressure measurements to get HIL closer to real conditions
Fixed wrong location of offset constant
flightgear: add configurable barometer offset
Merge remote-tracking branch 'upstream/master' into espeak

Conflicts:
	QGCExternalLibs.pri
	src/GAudioOutput.cc
	src/GAudioOutput.h
remove alsa asound library dependency comment
fix merge errors and unused-variable error
QGCMessageView: Extensive code cleanup and bug fixing.
Right-click menu works cleaner.
Coloring of output text is correct.
Output text now handles all severities of messages.
QGCMessageView: Added timestamps.
Message view: Forgot to remove debugging output.
Merge branch 'master' of github.com:mavlink/qgroundcontrol into message_view
Simplified formatting
message view improvements
espeak: cleanup
Readme.md: replace flite with espeak
espeak: remove c style zero initialize
espeak: remove comment
espeak: update readme
Fising the Message View and a Comment
New warnings from latest clang version

Removed completely unused variables. Ifdef’ed out variable which is
referenced from commented out code.