Added link tracks to all download options

[merwhite11]

Closes #9782

Adds link tracks to all download options in sidebar so that we can have a baseline reading of patron activity. This reading will then be used to compare the effectiveness of the work-in-progress Read dropdown redesign
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Testing

Click a download option and ensure that data for SideBar|Download is being recorded in stats.

Stakeholders

@cdrini @mekarpeles
@SivanC -- just letting you know about this one for when you want to compare SideBar|Download with your eventual ReadDropper|Download feature.

[mekarpeles]

We probably want different actions for the different download types. Instead of Sidebar, you might want to call that Download and then after the | the type

e.g. Download|HTML

[merwhite11]

@mekarpeles I see what you're saying. How then would we distinguish the Download | HTML in Sidebar from a click on Sivan's (future) Download | HTML in the Read dropdown?

[mekarpeles]

One option is to have something like Download|HTML_sidebar or DownloadSidebar|HTML. It depends how we want to split / roll-up the analytics.

Is it most useful to see the total number of downloads? The total number of downloads per type? Either way, so long as we segment/bucket the types we should be able to see what we need -- it just may take 2 queries + manual maths to get the totals we want.

I haven't spent much time thinking about the best solution. If we did Download|<Format>_<Location> then we'd get a total number of downloads and we'd be able to be able to easily add up the Format counts per Location. So that might be my strategy.

[merwhite11]

@mekarpeles I agree with the Download|<Format>_<Location> strategy. I will run by Drini before I make the changes.