* [simulator] Keyboard and mouse control adjustments:
~ Make kay/mouse navigation more consistent between radios and ensure keyboard events are always properly detected (eg. after clicking on a control);
* Fix mouse wheel direction for rotary encoder emulation (fixes https://github.com/opentx/opentx/issues/4160);
* Fix page up/down buttons on Horus (also #4160);
~ Horus rotary encoder can now be controlled with +/- keys (also keeps X/C, otherwise supersedes https://github.com/opentx/opentx/pull/4087 );
~ DEL key now another alternative for ESC/BKSP (brings all controls to number pad);
~ "=" key now acts same as "+" key (+ requires SHIFT in main row on most US keyboards);
* Fix controls direction when using mouse wheel over RC switches;
+ Add help text showing keyboard mappings for each radio type (activate on F1 key).
* [simulator] Enable mouse wheel scrolling on radios w/out a rotary encoder (acts as +/- keys on X9D, PU/DN keys on 9X).
