Add statistics collection backend

[JohannesLares]

• Add stats collection for record-views
• Add statistic queries
• Add Custom ES query class
• Upgrade invent-stats module to 1.0.0.a9

This PR creates a new feature to to collect statistics from record-views. Also new aggregations and statistics queries provided to get more insights about records and communities, such as:

• Community wide file-download total
• Community wide record-view total
• Total size of files in community
• Total amount of files in community
• Total amount of file-downloads in record

This has been tested and proven to work