Investigate and remove (or defer) unneeded CSS on page load

Some JIRA pages are loading as much as ~4100 unused CSS rules on page load.

There's a likelihood that some of the CSS supports form fields (e.g., single-select, multi-select, inline edit, etc.) or dynamic behaviours (e.g., dialogs, popups, etc.), and may need to be on the page at page load.

With those exceptions, JIRA should audit the CSS rules being loaded in the batch files and remove things that aren't strictly needed. This can reduce the page weight of each page, improving the app's performance.