Bug 838223 - lazy script loading and DB enumeration changes for faster startup

This pull request makes the gallery app start up a lot faster. It does the following:

load edit mode scripts on demand
load photo/video view scripts on demand
don't load gesture detector until we need it
don't load metadata parsing code unless needed
get rid of spinner on startup
move WebGL shaders from html file to ImageEditor.js
change the db enumeration algorithm for faster startup