Support Forums: Add link to active view in individual plugin and theme forums

[zoonini]

Could we add a link to the active view in each plugin and theme forum?

It's a view that displays all open threads in reverse chronological order, which is very helpful for theme and plugin support folks. Right now, you need to manually append /active to each individual plugin and theme forum to get the view. It would be more convenient and user-friendly to have the link exposed in the UI.

Examples:

​https://wordpress.org/support/plugin/akismet/active

​https://wordpress.org/support/theme/twentysixteen/active

Possible spot for the link:

[coffee2code]

In 4553:

Support Forums: Add 'Active Topics' link to sidebar for plugin and theme support forums.

Fixes #2202.