about screen shows build timestamp if running from /dist

addresses issue #7716 
this pull request replaces #7954

grunt task writes date to dist/config.json
uses local time
I chop off the long time zone section of the string because it wrapped to the next line on the about page

if running from src/ build timestamp line will be hidden

if running from /dist build timestamp is displayed

![withtimestamp](https://cloud.githubusercontent.com/assets/7686073/3170042/5b5dcd0a-ebad-11e3-8923-7c69b7a33226.PNG)