Added ElasticSearch Reader

ElasticSearch is a Lucene based indexer. When I am working with large datasets I often use an ElasticSearch cluster instead of a database since searching and retrieving data is MUCH faster than a database. Uses the RElasticSearch package. This is NOT a CRAN package, so don't know if it will interfere with travis-ci or submitting to CRAN.

So this raises some philosophical questions:

a) Do we want to add new readers to ProjectTemplate? Adding them willy-nilly can lead to an expanding code base and a maintenance nightmare down the road. If we do want to add readers to the Project should we develop a process of reviewing and vetting proposed readers and publish it on the ReadMe?

If we don't want to support new readers, we should add infrastructure so that users can add custom readers in their own project. This will minimize the number of forks people make just to add a reader of their own.

b) Do we want to allow dependencies on non-CRAN packages? Personally I like that github is becoming a viable option for package distribution and would like to encourage using packages from github. Any other views?

3) Fixed up the JDBC reader to behave in accordance with documentation.

Documentation claims that the JDBC reader will work if the jar file is included in the CLASSPATH. This only worked if classpath was included in the .sql file but left empty. Leaving out the classpath setting resulted in NULL being passed to the JDBC connection and throwing an error. It makes sense to me that if the jar file is already included in CLASSPATH then requiring an empty classpath in the .sql file is redundant.

Travis-CI is failing on this branch because RElasticSearch is not installed. Kirill, can you add this to .travis-ci.yml?