Uploading is now drag & drop (or click to browse) instead of a form;
folders can be created any time, not just during upload; files can be
dragged onto a folder to move them, or dropped elsewhere in the tree
to move back to the top level; files and folders can be deleted. Both
drag sources (an OS file drag and dragging an existing tree entry)
land on the same drop targets, told apart by a custom drag payload
type versus the browser's own "Files" type.
Also sort folders before files in the tree (previously interleaved
alphabetically).
Upload GPX files into a folder hierarchy (traversal-safe path
resolution against the store root), browse them in a tree panel, and
toggle each one's waypoints/tracks on the map. Waypoints render as
clickable points showing name, description and time; bare URLs in the
description are turned into safe links. GPX layers survive switching
between the Online/Offline base map, same as the radar overlay.
Adds rexml as an explicit dependency — it moved to a bundled gem in
this Ruby version and isn't picked up by Bundler otherwise.
randy