Fixes an infinite loop in the layoutModel atom synchronization that
would cause the atom to update indefinitely when the root node is
deleted.
Also adds a dedicated `disabled` flag for the IconButton decl so we can
disable the onClick handler when the button is disabled.
Also updates the Magnify toggle button to use this new flag, so that
when there's only one leaf in a layout, the magnify button is disabed.
move codeedit to directory. new useLongClick hook. show quick navigation for directoryview on longclick of folder icon. lots more generic
stuff for header
new fitaddon for xtermjs
more fixes for xtermjs scrollbars