UI Feature: Snap virtual walls to useful angles

[Hypfer]

As it is now, a virtual wall simply consists of two connected points which can be dragged manually.

Due to this imprecise movement, this results in them not being 100% aligned. For example if you intend to draw a horizontal line, you might end up with an angle of 178° or 181° which is mildly annoying.

Therefore, the idea would be to snap the lines to proper angles such as:

0°, 45°, 90° etc.

Whether or not more steps are required is tbd.
I'd assume that 95% of all use-cases only require these angles.

Maybe we could allow disabling the snapping altogether optionally.

The virtual wall class is defined here:

Valetudo/client/js/js-modules/locations.js

Line 367 in 3f4d844

export class VirtualWall {