chore(demo): re-structurize demos

A proposal for a demos structure.
* demo files are moved to the demo directory
* js files moved to the demo/js directory
* localization files moved to the demo/l10n directory
* fixed Grunt.js and .gitignore according to the new structure

A list of demos is not complete. There are some new demos and
some rewritten old demos.
Merge pull request #51 from DWand/chore-demo

re-structurize demos