Store requested / approval / rejection / closed dates

[dd32]

Currently the plugin directory stores the requested and approval dates for plugins, as it's useful for reporting we should continue to do so.

It probably makes sense to also include things such as the rejection and closed dates.

This would be made easier if we were using an Audit-log style plugin for keeping track of this.

[obenland]

In 3382:

Plugin Directory: Log plugin status changes.

We'll use post meta for now, long term we should be using an audit plugin
for this.

Fixes #1721.

[samuelsidler]

Milestone Plugin Directory v3 - M5 deleted