Proposal: Adding Rendering Performance Tests for Components

## What is in this pull request

The rendering performance tests are based on Chromium telemetry and help check performance regressions across commits. 
The useful metrics measured include
1. __Smoothness__ - measured by way of mean time to draw each frame while scrolling
2. __Page load time__ - measured using firstPaintTime and window.performance

Adding 'heavy' CSS like blurs or shadows, or javascript that does unnecessary re-painting affect these numbers and indicate performance regressions. The idea is to ensure that as more features are added to the CSS, the components themselves have good CSS and do not become slow. Hence, __performance regression testing as a part of continuous integration process__

## What has been added

A new grunt task has been added that generates temporary files, runs the performance tests for them in saucelabs and reports back the results. The results are stored in a CouchDB Database. The CouchApp in the same database is used to view this data over commits.

This is based on http://axemclion.github.com/bootstrap-perf and is inspired by the work done with http://bench.topcoat.io. 
To run the performance task, run `grunt connect perf`. I have not yet hooked it into travis yet, will do that once this proposal to add rendering tasks is accepted. 

## Things to note
1. The couchDB account is under my name and before the final merge, needs to be changed to a couchDB that bootstrap owns. 
2. The graph will be visible at `http://coucdbserver/databasename/_design/site/index.html`
2. When running locally, the commit number and job id are not available in environment variable. That is the reason that you do not see any graphs yet. Once integrated with travis, all this information will be populated, allowing for a more useful graph.