Add copy button to code blocks

[DunnCoding]

Currently there is no copy to clipboard button for code blocks within the documentation. The design proposed in #377 includes a copy button. We should look into how to implement the functionality for this.

[SueChaplain]

I think a good example of a page that would benefit from the copy to clipboard function is the new developing stacks page, where, as a stack developer I might want to copy the commands necessary to create a new stack and copy the basic stacks.yml file to get me going.