Navigator rework

[PiTheGuy]

Implements the navigator rework as described in #267.

• Navigation is now always relative to the cursor rather than maintaining a separate stored position.
• The navigator still wraps around when necessary.
• The navigator's index is still stored but is now only used for display purposes. It is updated accordingly when navigating.

[ix0rai]

thanks! i'll look into this soon

[ix0rai]

this feels a lot more reliable than the old version, thank you so much!