I noticed a bug when a plugin requires another plugin.

If eg a plugin named `Acc` requires a plugin named `Cli`, plugin `Acc` will be not activated because `Acc` will be always loaded before `Cli`. See https://github.com/piwik/piwik/blob/3.0.4-b2/core/Application/Kernel/PluginList.php#L113-L114 we always sort custom plugins alphabetically. However, it should respect a required plugin and make sure to load a required plugin first. In this case `Cli` before `Acc`.

In #11676 I implemented similar solution but is slower I would say. This solution should be quite a bit faster when having a few plugins installed.

@sgiehl @mattab maybe you guys have a better idea on how to fix it?

There is still an issue that `plugins/$pluginName/config/config.php` in each plugin is loaded alphabetically. It is to be discussed if a `config.php` of a required plugin should have less of a priority so that a plugin that requires another plugin, can overwrite a DI setting of the required plugin. Meaning ideally, the config for `Cli` would be loaded first, then `Acc` because `Acc` requires `Cli`. This way `Acc` could overwrite any DI setting from `Cli`. Currently, `config.php` files are loaded as they are defined in `config.ini.php` which is usually alphabetically because of https://github.com/piwik/piwik/blob/3.0.4-b2/core/Plugin/Manager.php#L209-L212 (if config file is writable and not changed manually).