Ensure file consistency using checksums

[exalate-issue-sync]

Stories

• As a user I want to be sure that uploads have not been corrupted in transit.

Acceptence criteria

• acceptance test suite for normal PUT initial checksum support for ocis cs3org/reva#1400
• acceptance test suite for chunked uploads (https://github.com/owncloud/core/blob/225cf25f85305f4a67cb766cf407e89be081c040/tests/acceptance/features/apiMain/checksums.feature#L58)
• acceptance test suite for uploading to shared files(https://github.com/owncloud/core/blob/225cf25f85305f4a67cb766cf407e89be081c040/tests/acceptance/features/apiMain/checksums.feature#L119)
• acceptance test suite for TUS checksumming extension? subtask: Add TUS checksumming tests #1599

[exalate-issue-sync]

Jörn Friedrich Dreyer commented: needs tus protocol clarifications, see https://jira.owncloud.com/browse/OCIS-1367