Add plugins dependency capability

[mattab]

In #4183 support is added for “require” piwik and / or a php version.
- Some plugins may also “require” other Piwik plugins (core or third party) to be installed at a particular minimum version.
- When a plugin has other required plugins, when possible, ask user & then install required plugins first, then this plugin.

As a result, it will be clean and almost error-free to use a plugin, as long as the developer set the “require” flags properly. This would be a subtle yet useful new feature.

[mattab]

When disabling plugins, other plugins that depend on the disabled plugins should be disabled. A confirmation message should be displayed for these plugins that are depended on by other plugins.

For example, the Goals plugin depends on the Referers plugin. If the Referers plugin is disabled, a message would be displayed "Disabling the Referers plugin will also disable the Goals plugins. Are you sure you want to disable the Referers and Goals plugins?"

[ThaDafinser]

+1 would just need this

[tsteur]

Is this a duplicate of #4485 ? Can we close this one?

[mattab]

correct