Build: Improve custom build module ordering and CSS production

Constructing a custom structure, theme, and combined CSS for a given value of the --modules command line parameter was missing. This PR implements that.

The order in which modules are specified on the command line is not necessarily correct. The order in which they are specified in js/jquery.mobile.js is correct. So far, js/jquery.mobile.js was being parsed using regular expressions to retrieve the list of modules as it appears in js/jquery.mobile.js. This PR improves upon that by retrieving the list from js/jquery.mobile.js by parsing the file using esprima.