Improve data exchange to filters

Once more, I improve the data exchange between controllers and filters:

1.  In the first version, I put the ID of the saved instance into the
    data model which was evaluated by filters such as LruFilters.
2.  In the second version, I remove the data exchange completely because
    it seemed to be fragile.  However, the ProjectFilters needed the ID
    to assign created instances to projects.
3.  Thus, now I store the created instance under the name
    "controllerInstance" (where "controller" is the name of the
    controller) in the request context which is evaluated by all
    filters, such as LruFilters, ViewFilters, and ProjectFilters.  The
    method to index and re-index instances for search is moved to
    ViewFilters, now.  This approach seems to be future-proof, because
    it allows new filters to obtain the instance from the request
    context and perform additional operations on it.