1620 deletion of child ontologies (#1748) * Make removed child ontologies "not present". * Scope default children association of acts_as_tree to present ontologies. * Show only present ontologies of this file. * Fix ontology factory. * Add cucumber features. * Fix restoring children. * Fix restoring a child ontology. * Add specs for restoring children. * Really fix restoring a child ontology. * Only save the ontology if it has changed or if it is a new record.

include ontology-class icons into fancy links.

add method to fetch logic-specific het. DOs - add a method to fetch the logic-specific heterogeneous Distributed Ontologies - Refactor duplicate code into own method (DRY) - Use "speaking" constants instead of seemingly arbitrary strings.

add passing code for logic specific DO fetching.

determine heterogeneous children with sql.

replace minimal queries with sql-based queries.

add display of heterogeneous ontologies in logics.

add minimal working versions for queries - since they rely on ruby's select method, they are quite slow and will be optimized by an sql-query later.

add code for homogeneous distributed ontology - add two methods to determine whether an ontology is heterogeneous or homogeneous.

Import of distributed ontologies works

XML parser adjusted to the new format