[Simulator] Asynchronous SimulatorInterface & a few new features. (#4738)

[Simulator] Asynchronous SimulatorInterface & a few new features. (#4738)

* [Simulator] Create RadioKeyWidget class for UI buttons & refactor ButtonsWidget; Refactor SimulatedUIWidget (and subtypes) to use new RadioKeyWidgets/ButtonsWidget; Centralize help text for key mappings and get creative with some icons; Simplify some radio UI setups with rectangular buttons.

* [Simulator] Convert all simulator data I/O to signals/slots mechanism:
    * SimulatorInterface/OpenTxSimulator:
       - Now inherits from QObject to allow signal/slot interface;
       - Allows data exchange on a per-item basis (eg. each I/O value is treated separately instead of sending whole arrays or structs of data);
       - Checks for data changes and only emits signals when change is detected (GUI can now assume only new values are being sent);
       - Manages its own 10ms timer (doesn't rely on GUI to do that);
       - Sends "heartbeat" signals @ 1Hz for status monitoring;
    * Simulator GUI:
       - All data is exchanged between GUI elements as well as SimulatorInterface via signals/slots using standardized methods;
       - Data is sent immediately, and only, when actually changed (eg. a control is moved) instead of in bulk at specific time intervals;
       - Similarly, an asynchronous method is used for reading incoming data, w/out timers or loops;
       - Improve VirtualJoystickWidget to be more encapsulated and configurable;
       - Pause telemetry simulator if window is hidden;

* [Simulator] Move SimulatorInterface instance to separate thread, ensure safe asynchronous operations & proper timer interactions; Protect/remove some functions, & reorganize the order (cosmetics).

* [Simulator] Traces are now delivered to OpenTxSimulator and one or more QIODevice(s) can be added as recipient(s); Add SimulatorInterface::getCapability() for compile-time settings; Remove reversed POT1/SLIDER1 mixer exception (Taranis) requirement for SIMU; Fix plus/minus key delay on wheel event w/out encoder.

* [Simulator] Add current knob/slider/trim input value in tool-tips (KnobWidget and SliderWidget).

* [Simulator] Fix trims widget internal value not properly updating, and remove trim influence on virtual joystick X/Y value display (closes #4671).

* [SimulatorInterface] Add handling of transmitter input voltage, including a rough conversion of volts to ADC value for different boards, and default battery volts lookup function; Clear analogs array before starting.

* [Simulator] Add SimulatorInterface::init() method to separate pre-startup tasks; Report actual trim range, not just extended on/off; Change how radio widget states are restored; VirtualJoystickWidget: Connect trim changes directly from simulator, connect joystick events directly, report stick mode directly instead of setting values/constraints externally.

* [Simulator] Calculate default Tx V input based on configured range in radio settings (or warning V+2 for radios which don't support a range).

* [Simulator] Add functional aux. trims for Horus (closes #4699).

* [Companion] Remove problematic QMessageLogContext from AppDebugMessageHandler::messageOutput().

* [Simulator] Prevent trim change via slider if disabled for flight mode (closes #4600).

* [OpenTxSimulator] Fixes for Qt < 5.4.

* [OpenTxSimulator] Fix slot name.