feat: new SVG assets for circle toolhead controls

[pedrolamas]

Replaces the current SVG assets that have been ported from Mainsail with news ones designed from scratch.

Some relevant changes:

• all assets are "static" (as in they are designed to be used "in situ" instead of having a global definitions and then applying runtime transformations to the asset)
• all MDI icons have been resized to have same dimensions
• new "xy center" icon (based on existing "focus" MDI icon)
• new "stepper motors off" icon (tries to resemble a stepper motor when looked from above)
• the 4 corner buttons have been reoriented to be aligned with the user perspective (thus resembling more the original Pronterface interface)

[vajonam]

looks good!