Suggested feature: In polyline, let user draw a line that is parallel with a major axis

[raindropsfromsky]

When we draw a polyline, we cannot draw a line that is exactly aligned with a major axis (x, y or z). If the user presses SHFT while dragging the mouse, align the line with the nearest major axis.

This is just like how PowerPoint (or Libreoffice Impress) allows us to create a perfectly horizontal/vertical line by pressing SHFT while we drag the mouse.

In addition, if the user presses CTRL and drags the mouse, the line angle should be constrained to multiple of 15 degrees with respect to a major axis.