Implement multi-range slice queries for CQL storage implementation

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Discussion: #3812

As for now JanusGraph can fetch requested properties either using a separate slice query per each property or using a single slice query to fetch all vertex properties. The user should always weight pros and cons of each approach and decide how they want to fetch those properties.
With multiple ranges per single slice query it will be possible to fetch only requested set of properties in a single slice query. Thus, the user won't need to decide between trade-offs of each solution.

Start by reading the linked discussion in #3812 and then locate the CQL storage implementation in the JanusGraph repository. The goal is a single slice query that supports multiple ranges and fetches only the requested properties, rather than requiring one query per property or one query for all properties.

Written by the indexing model from the issue text.