Changed the onclick handler to trigger the impress:console:open event
and not use the impressConsole() global function any more. The latter
is considered deprecated now that impressConsole is integrated into
impress.js itself.
Also catch some errors that appear in event handlers when the target
for the click event was immediately removed from DOM.
Fixes#651
* Source files are under src/
* js/impress.js is now generated, but remains part of the repo (so it just works)
* npm run build
* build.js uses buildify node module
* Break out navigation and resize plugins from core src/impress.js file
