make workspace sidebar use a singleton instead of inferring

EpubContainer for gh-book and WorkspaceRoot for atc
add code to hide Book Picker title
if model does not have .findDescendantDFS then use the original model
for pointer events splice in the pointer model

this causes problems when filteredCollection tries to keep its
collection in sync
remove unused (and poorly defined) trigger

it should at the very least send @ as an argument
Merge branch 'master' into atc-root-singleton

Conflicts:
	scripts/gh-book/app.coffee
Merge branch 'master' into atc-root-singleton

Conflicts:
	scripts/gh-book/app.coffee
Merge remote-tracking branch 'origin/master' into atc-root-singleton
add fix so new Modules are added properly to the Workspace
resset content view between renders
refactor content pane styles when content is empty
allow deleting currently active module
TocPointerNode.getRoot() returns the OPF file instead of the EPUBContainer
Implement simple migration view.

This includes a table migration as well, for removing captions on tables.
look up the root node when calling addChild
merge from master
Add a slight delay for dragging to start.

A quarter of a second avoids that irritating problem where things are
accidentally dragged into another chapter.
update version of less
fix adding a new book. no longer throws an error
disable save when new book is added