Add move-outline-to-first/last-child commands

[edreamleo]

move-outline-to-first-child is convenient when a creating a section.

With default settings Leo creates the section definition node as the last child of its parent. If a node has many children it is surprisingly inconvenient to move (manually!) the newly-created node to be the first child of its parent.

move-outline-to-last-child is less useful (with default settings), but it should be added as a companion command.

These commands do nothing if a hoist is in effect.

Aha! The extract commands should create section definition nodes as the first child of their parent node.

[edreamleo]

Closed via PR #3532.