Improve fly mode with new shortcut keys and mouse wheel

Implement following to help the user to work faster in fly mode:

Keystrokes

• Press SHIFT down to move 30% faster
• Press ALT down to move 30% slower

Mouse wheel

• Enable use of mouse wheel while in fly mode to control the speed. Rolling the wheel would make speed slower or faster.
• When rolling, show the value of the slider on the screen. Visual suggestion here:
  https://www.figma.com/file/80F3En6Rhehbi7PkWewPCI/3D-Editor?type=design&node-id=52%3A697&mode=design&t=lui0jXuKtrD5s1ra-1