- Add boilerplate/infrastructure for argument parsing, hotkeys, event handling
- Adds the "MovePane" function that finds the focused pane, and then tries to find
  a pane that is visually adjacent to according to direction.
- First pass at the "SwapPanes" function that swaps the tree location of two panes
- First "working" version of helpers _FindFocusAndNeighbor and _FindNeighborFromFocus
  that search the tree for the currently focused pane, and then climbs back up the tree
  to try to find a sibling pane that is adjacent to it. The actual `_IsAdjacent' function
  is just a stub.
  Once working these functions could be utilized to also solve GH issue 2398.

- FindFocusAndNeighbor and FindNeighborFromFocus now record a relative offset of
  their children.
- _IsAdjacent now properly tests if two panes, given eachs' relative offsets
  are adjacent according to direction.

…olumn locations to the correct elements.

…anes to find parents. Add checks to make sure there are enough panes to actually find the previous one.