Added performancestatistics.js - save load times from performance.timings to local storage, run simple statistics and show to console)

`performancestatistics.js` is a snippet to save `performance.timing` data to `localStorage`, create simple statistics (mean load time & stddev.) and show results in console.

1. Calculate a series of timings from `window.performance`. *this will be one data point*
1. Save data point by location path & search as JSONfied array to `localStorage`
   ![bildschirmfoto 2013-07-24 um 16 54 45](https://f.cloud.github.com/assets/1786188/849245/118e6f42-f471-11e2-9c49-bd954029d7e3.png)
1. Take all data points, calculate mean & std. deviation, push to console
  ![bildschirmfoto 2013-07-24 um 16 53 48](https://f.cloud.github.com/assets/1786188/849246/119fd55c-f471-11e2-9078-735c6798aab6.png)

**Result:** running this snippet after each "cache cleared" page load, will give some simple statistics on page load timings