wrappers to the DDR removables(_mounted) funcs with added info

The removables_mounted function adds a flag indicating whether
the removable is the target of the MEDIA_BASE symlink.
Note: Had to rename some vars in storage.views to prevent name
clashes.
don't need to specify path for rm_media_symlink
rework active-removable form; add ability to select active rem
split the storage-index view into several simpler view

This view was handling GET and POST for mounting and unmounting
devices as well as changing the active device, and was getting
convoluted.