Combines pull request #21 and #25 - Enables force, warnings do not stop build, and reporting to console is limited if another reporter is present

- Merges pull #21, #25


- Providing ```options: { force: true }``` prevents csslint from returning false and thus stopping further tasks
- If another reporter is present, console logging is limited to summarization on a file level
- CssLint warnings are not constituted as errors so the task does not fail