Reimplement layout using Flexbox and Bootstrap

- rewrite the layout and css by using flexbox and bootstrap
- split Player and Application out from core.js
remove main.css
fix left pane height
save, open and url_texture select dialogs with file-select-control
add mocha test for file-select-control; load jquery, handlebars from node_modules, remove them from vendor/, and serve node_modules folder
add jsdom package to dev dependencies
fix jquery to 2.1.0
load dialogs for audio, json, texture, video working
fix breadcrumb
Set overflow for the left panel to auto, and - for the info panel, shrinked the font size. This fixes the box jitter on node -> slot hover.
Fixed breadcrumb style and logic.
Fixed plugin UI table borders and plugin UI vertical alignment.
Fixed header row height.
Fixed connection rendering.
move index.html to editor.html