Add watch support + use grunt variable expansion

* `lineman run` will now catch linting problems as you work 
* Spec files will now trigger lint failures
* Switched to the familiar (at least relative to the rest of lineman), string-variable expansion version of specifying glob references. This is nice because it expands at `grunt.initConfig`-time, which is assured to be after *each-and-every* plugin has loaded and modified the configuration struct. The previous approach is at risk of missing a modification to the globs based on load order of the plugins.