Tracking logs and a workbench scenario

[ericouyang]

Revised event names:

xblock.image-explorer.loaded xblock.image-explorer.hotspot.opened xblock.image-explorer.hotspot.closed

[aboudreault]

LGTM, when ericouyang comments are addressed.

[antoviaque]

Adding another good remark from @ericouyang which applies to all the XBlocks to which we're adding events:

"_One thing that I do think is worth implementing is for the original show events (now called loaded) to be triggered in javascript once the xblock has finished loading on the client side, rather than on the server-side in student_view_"

[dragonfi]

@antoviaque Yep, loaded does clarify the meaning, I can do that.

[dragonfi]

@ericouyang @antoviaque PR updated with suggested changes.

[ericouyang]

@dragonfi LGTM!