add collapsable and copiable code block support about org-page

[sillykelvin]

I did some research on this topic, it is not so hard to implement it, we need some efforts:

1. write some javascript code. This will introduce a new dependency jQuery (of course it can be implemented without jquery, but will be much easier if uses jquery)
2. need a small hack on op/export-as-html function, as the original function provides little support for javascript
3. write some CSS code, to make the layout looks better

I have finished the first two items, but I am not good at CSS, so currently I am adjusting the style described in item 3.
After finished, I will push the commits to the devel branch.