Improve main page styling

This MR started by addressing backwards-compatibility issues (https://code.librehq.com/ots/clients/lfc/torque-tracker/-/issues/300) but moved on to a longer list of improvements.

• Changes the expected CSS class/ID structure — see https://code.librehq.com/ots/clients/lfc/torque-tracker/-/work_items/301#note_10994
• Remove page header coloring; this is now a per-wiki customization through Common.css
• Improves page header padding for situations when there is no hero copy
• Expands supported stage count from 5 to 10
• Adds max-width to simple maps on the main page
• Adds instructions to CSS for customizing main page

Closes https://code.librehq.com/ots/clients/lfc/torque-tracker/-/issues/300

Addresses https://code.librehq.com/ots/clients/lfc/torque-tracker/-/work_items/301