Fixes the following issues:
* Selection behavior
* Component selection is by header click only
* Newly created blocks within a unit should be selected on creation/save, appear selected, and have their sidebar open
* Some long text components seem to display at the default height rather than a longer height
* Within the full-page unit view, the "add to collection" overflow menu item on components does not seem to work/only opens the sidebar.
* Draft status indicator text is not vertically centered with icon
* When reordering, dragging a short component past a long component often causes a strange stutter effect.
* When dragging to reorder a component, moving quickly or scrolling often causes the drag handle to be lost / causes the block to jump somewhere else
* Reordering may not consistently support a keyboard-accessible option to change order, like in course authoring
* Tag button on component header opens the old tag side pane
Reorders components in unit page via drag and drop. This PR also refactors and moves draggable list and sortable item components to appropriate location.
Course authors will be affected by this change.
