409 polyfill refactor

PR Highlights:
- Moves `sprockets_better_errors` gem to development group and performs comment formatting (capitalization and missing periods) to gemfile.
- Moves IE-specific polyfills out of requirejs pipeline and sets up IE8 and IE9 specific manifests that include polyfills needed for those browsers, which are conditionally included before all other scripts (but after Modernizr).
- Moves Modernizr to its own include in the top of the head to fit with Modernizr's inclusion practices and avoid having the complication of shimming Modernizr and handling the dependency order of Modernizr plugins.
- Removes selectivizr and html5shiv gems in favor of directly including those scripts via the ie8/9 manifests as those scripts are only needed for older browsers and don't warrant separate handling to other polyfills in their own gems.
- Removes hasOwnProperty method in for ... in loops in favor of checking sought after method directly, as hasOwnProperty throws an error in IE8 on Elements.
- Adds console.log fix for older browsers (fixes #404)
- Adds directive for rails asset pipeline to handle map markers (fixes #433)