#4 Chain selection and editing

[Tobias Schlemmer]

I'd like a comfortable way for chain based lattice editing. This meight work as following:

1. Selecting one node selects the infimum irreducibles above or below as well as the corresponding ideals.
2. Dragging a node will cause the wohle chain to move, the dragged node follows the mouse. If there are irreducibles above: the movement is evenly distributed on them. The per irreducible movement will be applied additionally to all irreducibles below.
3. All reducible nodes below them are moved by the sum of the movements of the nodes above them. The look and feel shoul be somehow as moving a whing.