Remove information about the email from the basic user information

[nmanovic]

Motivation and context

Now CVAT by default can return information about users (/api/v1/users end point). It contains basic information about the user including the e-mail. Need to hide e-mail by default.

How has this been tested?

Tests for cvat server were modified to address the change.

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT

[coveralls]

Pull Request Test Coverage Report for Build 5406

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 65.657%

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Files with Coverage Reduction	New Missed Lines	%
cvat/apps/engine/media_extractors.py	2	77.06%

Totals
Change from base Build 5398:	0.03%
Covered Lines:	10836
Relevant Lines:	16101

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💛 - Coveralls