Implemented lazy loading for resource tab

[noisecapella]

Fixes #770

[jamiefolsom]

I'll look at this one.

[jamiefolsom]

• Functionality
• Code
• Tests pass
• Questions

[jamiefolsom]

@noisecapella -- should we set the active tab in the panel to the vocabulary tab every time we load the panel, so that XML is not loaded unless explicitly requested?

Steps: First time I click on an LR, the panel opens, with vocab active. All good. Click on XML tab. Then close the panel. Then open another LR, and the XML tab is still selected. Might be we're loading that content too eagerly.

[noisecapella]

That's a good idea, I'll make that change

[jamiefolsom]

Nit: add a newline here.

[jamiefolsom]

General comment, perhaps unavoidable, but listing.js is getting hard to navigate, at almost 600 lines of js. Time to consider refactoring it?

[noisecapella]

Already doing it #797

[jamiefolsom]

Cool.

[jamiefolsom]

Could this...

[jamiefolsom]

All my notes are optional. Looks good and works well. 👍 from me.

[noisecapella]

Ok, it should now load the resource tab whenever the panel opens

[jamiefolsom]

Nice. Works well. 👍