- class the #sidebar itself as collapsed not the #id-container
- the #sidebar is the selection, so just use `selection` instead of
`var sidebar = d3_select('#sidebar');`
(which conflicts with the closure `sidebar()` function)
- have separate functions `expand` `collapse` `toggle` rather than a
`toggle(shouldCollapse)`
- Dragging the sidebar below a minimum size collapses it
- A button in the top toolbar lets you uncollapse the sidebar, complete with icon and tooltip
- Double-clicking the divider toggles the sidebar collapse
- Collapse-toggling is animated
- Selecting a feature or ending an add-feature mode auto-opens the sidebar
- Photoviewer UI has been moved from init.js to photoviewer.js
- The photoviewer now has a slight margin to set it away from the sidebar
- The undo/redo, save, and progress indicator controls are now floated to the right
- The save count has been redesigned to visually integrate with the save button
- When the sidebar is collapsed, the mode buttons are centered
- Full right-to-left layout support for all of the above
