UMD tests

As suggested in #13811, here are tests/examples of using Bootstrap with RequireJS and Browserify. Both working with the concatenated file and using individual plugins is being demonstrated.

This also includes a fix for #13812, which removes the module definitions from the individual plugins and wraps them all in one big factory function. It's pretty hacky so I'd like to get feedback on it.

/cc @fat @cvrebert @XhmikosR
`process` runs before each file is added to the concatenated output, so unless the UMD stuff is included twice in a source file, I don't see a problem.