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

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.

Don't read out seconds since last connection on connection regain

Allow the Primary Flight Display widget to be resized smaller than is currently possible

Missed phonon-devel package from build instructions for Fedora.

The Fullscreen/Normal menu items in the main window are now checkable.

Replaced hard-coded severity values with proper MAV_SEVERITY_* macros.

Removed constant debugging output from scanning for serial ports.

Fix for #647

Replaced with only 1 output message with the result of the first serial port scan.

In the logplayer, the data stream is read ahead for messages, which is used to determine the size of the output bytearrays. Previously, this wasn't done correctly resulting in non-ideal behavior. Now, the next message is scanned properly, so the only bytearrays that are emitted from QGCMAVLinkLogPlayer are MAVLink messages in their entirety. This also has the benefit of skipping invalid/corrupted messages in the log that's being played back.

Refactored QGC::groundTime*() functions to be simpler.

Master

Conflicts:
	qgroundcontrol.pro

Readme: dependencies for Arch Linux

Because the indexes into the stackedwidget are all wrong