Integrate ZeroClipboard to easily copy code snippets

**What I am trying to solve?**

Usually people will copy the code snippets from Bootstrap documentation and edit according to their need. For bigger section of snippets on selecting the code, page scrolls and unwanted texts are selected which makes copying process little bit complex. To overcome the difficulty and to easily copy the code snippets I have integrated the https://github.com/zeroclipboard/zeroclipboard.

**Completed**
  * Copy to clipboard functionality
  * Tooltip based notification for successful copy, flash problem

For demonstration purpose I have added the copy to clipboard in few places of the documentation. Also I have attached the few screenshots for the core team review.

**Browser Support**
Even though the library depends on the Flash it gives better browser support. Please refer https://github.com/zeroclipboard/zeroclipboard#support for browser support.

**Screenshots**

![copy-to-clipboard-highlight](https://f.cloud.github.com/assets/528129/1810600/9559a8fc-6e2c-11e3-945f-65ae2dd27b37.png)

![copy-to-clipboard-bs-example-and-highlight](https://f.cloud.github.com/assets/528129/1810592/311631e4-6e2c-11e3-8ac2-f2b1ec6ca935.png)

![copy-to-clipboard-mobile](https://f.cloud.github.com/assets/528129/1810593/379400dc-6e2c-11e3-97eb-ed119e5287d8.png)