FlightMenu sliders, customisablility

FlightMenu now uses sliders. Please note that clicking too near the
centre of the heading slider will fall inside the (obscured) white
circle, trigger mode switch, and hide the menu. Speed cannot be set.

FlightMenu:
-changed _Indicators to represent normalised position on the scale
+reduces conversions per frame
+heading now stored in radians to reduce trig. conversions
-added multScale() to convert normalised scale to full scale value
-added inIndicator() to detect if mouse is in indicator, corrected for
flight position
-mousePressed() now detects sliders clicked
-mouseDragged() now changes slider positions
-mouseReleased() now triggers events for sliders
-event_ functions for sliders now set values
+excepting speed, where the current architecture does not support this
properly; will still print to console
-renamed aLabelFont -> labelFont
-renamed aButtonFont -> buttonFont
-renamed aLabelColor -> labelColor
-renamed aButtonColor -> buttonColor
-added getters/setters for label fonts/colours for buttons/labels
Merge branch 'master' of https://github.com/SEPRGroup/SEPR3Project