Implement solr query abstraction & transparent predicate pushdown

[adersberger]

• Solr query abstraction like in the AIR project (maybe reuse this)
• Provide a builder to create time series specific solr queries including the Chronix-specific Solr extensions
• Modify the basic RDD aggregations (min, max, ...) to delegate to Solr aggregations (enhanced predicate pushdown)
• Add the ability for MetricTimeSeries / TimeSeries to carry pre-aggregated values additional to a time series e.g. min/max/avg