How to cite should use buttons not links

> The current How To Cite pattern uses <a> elements which provide a non-JS fallback that delivers HTML code. This should be changed to use <button> elements for more semantic and accessible controls.
> 
> See: https://github.com/pkp/ojs/pull/2465#issuecomment-534038455

Issue copied from https://github.com/pkp/theme-components/issues/2.