Switches us to concat_sourcemap

[searls]

Resolves #187

Could use a little review maybe, especially b/c this will impact existing plugins, templates, and projects that have already disabled the concat task.

[searls]

FYI, the lineman-angular plugin (and anything else we've published already on concat_sourcemap will need to be remediated like so:

• Patch bump and lock to the current minor version of lineman
• Minor bump and upgrade to the lineman that introduces this feature
• Right now, it uses an ngtemplates file property name to include those, but that'll need to be replaced by overriding files.template.generated instead, which strikes me as more proper anyway.