PSR-12 coding style

respect conf['target'] for Docs and Bugs links

fix #2912

better variable name

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Update de, de-informal

sort plugins in plugin_list()

Revert "eliminate access to global $plugin_controller"

This reverts commit 2b1bb8ffafe5d72c35b81659b1d96b8dc19f0de3.

eliminate access to global $plugin_controller

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fixed bug in extension cli when installing multiple plugins

replaced deprecated utf8 functions

For now this uses full qualified namespaces, sensible imports may come
later.

added filter to extension listing in CLI component

fix color for noninstalled extensions

show disabled extensions in gray

warn about inaccessible repo api

bugfix: access check was never cached

Now the API ping result is cached for 10 minutes and can be refreshed
using the purge parameter as intended.

First go on a CLI component for the extension manager

This allows managing plugins from the command line which is useful in
automatic deployments (eg. through salt or ansible).

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Move list of plugin types to plugin controller constant

There is no need to have them in a global variable.

moved plugin controller to Extension namespace