Add native version checks (php, core, multisite) for plugins

[cfoellmann]

Additional core plugin headers for compatibility filtering on plugin.php.
Fully optional like Network: True

Headers:

$plugin_data['Core'] // The minimum WordPress version required.
$plugin_data['PHP'] // The minimal PHP version required.

Additional view on plugins.php:

plugins.php?plugin_status=incompatible // listing all incompatible plugins (removed from ?plugin_status=all)

DONE:

• ADDED headers: Core, PHP, Multisite
• ADDED checks for headers values: is_plugin_compatible() + separate checks for the three single headers
• ADDED view "incompatible" to plugins.php
• UNSET incompatible plugins from view "all"
• ADDED option to "Delete" plugin on view "incompatible"

TODO:

• ADD function to remove incompatible plugins from mu-plugins loading
• ADD display of compatibility issues details for each single plugin

Direct checkout: ​https://github.com/cfoellmann/WordPress/tree/headers
Patch(es): Attached

[cfoellmann]

patch-0.1

[jdgrimes]

Looks like this might be a duplicate of #26909.

[jeremyfelt]

Agreed, and has a patch as well.

I think this is great progress, @cfoellmann. Can you add a comment and your patch to #26909 for further discussion there?