Add a tool activate manager

This PR adds a tool activate manager. The manager is a singleton that handles the activation of plugins that are part of "activate toggle groups".

The goal of this work is to fix an [issue](https://github.com/camptocamp/sitn_c2cgeoportal/issues/150) in the sitn_c2cgeoportal project, where there's no way to deactivate the GetFeature's WMS GFI click control. With this PR plugins can deactivate and reactivate the GetFeature's WMS GFI click control when needed. The unit tests show how it works.

Please review.