Solr indexer improvement

This is an alternative for PR #368 

Use the near real time searching for index consumer means that documents are available for search almost immediately after being indexed.Softcommit is used this will refresh the view of the index faster, but without guarantees that the document is stably stored, use tlog to mantains the history and autoCommit configuration will do the rest every 15 minutes so it will flush recent index changes to stable storage. The behaviour can be modified by turn off the index.commit please see https://github.com/lap82/DSpace/commit/cb4468b85bca3c153a9686ba51ac34f85beb5940#diff-835d88df2862c3e3d90a212f74177f00R20

https://jira.duraspace.org/browse/DS-1715