Add configuration option to omit compressed files that are larger than the original

When a compression results in a larger file size than the source, I would like to skip compression on that file and include the raw source in the generated output.

A configuration property is more flexible and preferable to manually excluding files with this result.

Example (actually 100.5%):
```
[INFO] jquery.scrollable.min.js (101050b) -> jquery.scrollable.min.js (101583b)[100%]
```

With plugin version 1.1, the compressed file was actually 102% of the original size.