Move multiple selected Spots simultanously in BDV

[stefanhahmann]

User Story

As a user of Mastodon, I currently have the possibility to move a single Spot in BDV using Mouse-Hover + Space. However, sometimes, I would like to apply the same relative movement to multiple spots at the same time, e.g. all currently selected spots.
Thus, I would like to have another Keyboard Shortcut, e.g. Mouse-Hover + Space + Shift to enable this behavior.

Acceptance criteria

1. Add new Keyboard Shortcut
2. Behavior implemented that when the Keyboard shortcut is pressed and the mouse is hovered over one of the selected cell, all other selected cells are moved with the same relative movement.

Open Questions:

1. How should the behavior be, if there are multiple spots on top of each other and they are mouse-hovered at the same time.