Refactor pub/sub to localize events

[arthurian]

This PR refactors the event system in Mirador so that instead of publishing/subscribing to the global jQuery object, events are published/subscribed to an instance of Mirador.EventEmitter that belongs to Mirador. This is a first step to making it possible to have multiple instances of Mirador on the page (i.e. #904).

This PR touches quite a few source files in the release2.1 branch:

$ egrep -r 'jQuery\.(publish|subscribe|unsubscribe)' ./js/src | cut -d ":" -f1 | sort | uniq
./js/src/annotations/annotationTooltip.js
./js/src/annotations/catchEndpoint.js
./js/src/annotations/osd-region-draw-tool.js
./js/src/annotations/osd-svg-overlay.js
./js/src/utils/saveController.js
./js/src/viewer.js
./js/src/viewer/bookmarkPanel.js
./js/src/viewer/mainMenu.js
./js/src/viewer/manifestList.js
./js/src/viewer/manifestListItem.js
./js/src/viewer/manifestLoadStatusIndicator.js
./js/src/viewer/manifestsPanel.js
./js/src/viewer/workspacePanel.js
./js/src/widgets/annotationsLayer.js
./js/src/widgets/annotationsTab.js
./js/src/widgets/bookView.js
./js/src/widgets/contextControls.js
./js/src/widgets/hud.js
./js/src/widgets/imageView.js
./js/src/widgets/layersTab.js
./js/src/widgets/sidePanel.js
./js/src/widgets/tabs.js
./js/src/widgets/thumbnailsView.js
./js/src/widgets/toc.js
./js/src/workspace.js
./js/src/workspaces/slot.js
./js/src/workspaces/window.js

@rsinghal @aeschylus Not sure if you guys already started this on your own or not, so I figured I'd finish what I started last week and throw this up here for you to take a look at.

[rsinghal]

This looks good to me. @aeschylus did you start something like this already, or can we merge?