Update Elasticsearch Configuration
This patch updates the meachanism of how Opencast's internal
Elasticsearch is configured. It moves most of the configuration into the
bundle resources and mostly unifies the externalapi and adminui index
Reasons for the change are:
1. A lot of the exposed configuration options were actually fixed
settings and changing them could cause errors in Opencast. In other
words, there was nothing to configure at all.
2. The current configuration was mixing node and index configuration
which is no longer allowed starting with Elasticsearch 5.0. This
patch properly separates these settings.
3. All relevant configuration setting for both indexes were just
duplicated. Even worse, they had to be since the main node and some
index settings would only be loaded from one configuration location
and not defining it twice could lead to inconsistent behaviour of
Opencast after restarts.