Views style plugin for the completion bar

Make a views style plugin that can output a completion bar for a set of fields defined with views. Right now, you have the possibility to output the percentage for a single task using a bar. You don't have the option to output the accumulated percentage for a series of tasks using a bar. This way, you could perfectly replicate the completion bar block using views.

See #578784: Tasks show up even if unpublished that describes the original problem.