source link id is not unique if multiple animints on same page

[tdhock]

source link id is always a_source_href which could be problematic if there is more than one animint on the same page. fix would be to either change id to class, or append plot id to source link id. In the example above the plot id is "plot" so the button id prefixes that, "plot_show_hide_animation_controls" but the source link does not.