Update media extractors

[zhiltsov-max]

Motivation and context

Follow up for #2141

• Added PDF import tests
• Fixed Loading PDF. RAM consumption.  #940
• Fixed a problem with pdf cached chunks - after the first interpreter exit, extracted files were removed, making it impossible to recreate chunks
• Refactored some code

zip - need to test if extracting is really necessary

How has this been tested?

Unit tests, manual tests

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]

Coverage increased (+0.1%) to 65.505% when pulling b72fd19 on zm/update-extractors into c2b17a0 on develop.

[nmanovic]

@zhiltsov-max , could you please help to fix merge conflicts?

[nmanovic]

@Marishka17 , could you please review and test the PR?

[bsekachev]

@zhiltsov-max @Marishka17 @azhavoro What is status of this PR? Can me merge it?