Import roaring endpoint accepts a list of views

[yuce]

Overview

• Adds a protobuf message for passing an ImportRoaringRequest which sends view data together with import options.
• Moved Clear import option from the query arg to the protobuf message

TODO: Need to update an handler test so it posts encoded ImportRoaringRequest data. Fixed handlers tests.

Fixes #1716

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[yuce]

@travisturner Can you approve this again? I've added a check for empty data and merged with master which removed your approval review.