Configure a crawler_site_id by default.

[jone]

ftw.crawler now supports to configure a crawler_site_id. This change adds such a field for all solr cores by default. See 4teamwork/ftw.crawler#9

By adding the crawler_site_id field to the core template, all solr installation based on this buildout config will automatically receive the field for all cores, making it easier for developers to adapt to this feature.
It isn't necessary to have the field on regulare cores, but it is easier to add it to all cores in ftw-buildouts than to add the field in each project separately.

config-version:
The collective.recipe.solrinstance does not properly update the configuration: it only reinstalls when values of its part change. When configurations of the cores change, those changes are not in the solrinstance part and thus the recipe does not reinstall and the change is not applied.
As workaround we introduce a config-version value which is simply incremented and will trigger a reinstall of the solr part whenever incremented.

[maethu]

👍 Looks good to me.