Plugin Directory Admin: Improve messaging for reviewers

[Ipstenu]

After using the messaging for a while, it became obvious that the red/green was not enough of a color differential. Plus we don't WANT those alerts to be dismissible.

Attached to this is a patch that changes the alerts to notices (i.e the non dismissible). It also changes the colors.

• Red: Rejected, closed
• Yellow/Orange: pending, disabled
• Blue: Draft
• Green: Approved and waiting for code upload

In doing this, I broke apart the draft/pending alerts, which pointed out the flaw. We left in code for the original original plan to support non-admins on the back end. We won't be doing this anymore so I cleaned that up and made it smaller.

[Ipstenu]

Better messages

[SergeyBiryukov]

Tested 2693.diff​, looks good :)

[Otto42]

In 5271:

Plugin Directory: Better messages for reviewers, more color, make life prettier. Props @ipstenu. Fixes #2693