Plugin Directory: Improve Advanced / Danger Zone visibility

[Ipstenu]

Changes in this:

1. Break out the Danger Zone so that you can only see it's even a section if it's YOUR plugin (this will reduce FUD from end users on the Advanced Tab)

This involves moving the Advanced and Danger Zones to their own functions, plus an repeat why-closed message if the plugin is, in fact, already closed.

2. Clarify some language about why you cannot close your big plugins.

3. Soften language about 'maliciously' changing owners. Likely it's always going to an honest mistake. And since we track who does it and when, we'll be able to untangle and chastize.

[Otto42]

In 9784:

Plugins: Reorg danger zone to separate functions, hide bits from users that don't need to see them. Fixes #5177