Gestures on PDFs

[nucleogenesis]

Summary

Adds hammerjs and in PDF Renderer make use of it to handle pinch-zoom gestures on mobile.

Does not work on iOS because Apple's pinch zooming always zooms the whole window without regard for any kind of meta viewport settings (ie, maximum-scale or user-scalable).

However, it works on Android.

Basically, a pinch will call the same zoomIn or zoomOut function as tapping the + and - buttons do. They're throttled to 1 second to avoid accidentally zooming all the way in with one pinch.

NOTE: Not tested in a real life proper "app context" running the Android app - but still a valuable addition for non-app users who do use android devices anyway.

Reviewer guidance

Open a PDF using an Android device and pinch zoom in and out.

Testing this without an actual device is a pain - but if you use Genymotion read this (it wasn't perfect for me, but good enough early on)

References

#3710

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Contributor Checklist

PR process:

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Testing:

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

Reviewer Checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[codecov]

Codecov Report

Merging #6996 into app-support will decrease coverage by 0.14%.
The diff coverage is 0.00%.

Impacted Files	Coverage Δ
...s/pdf_viewer/assets/src/views/PdfRendererIndex.vue	0.00% <0.00%> (ø)
...plugins/user/assets/src/views/SignInPage/index.vue	29.10% <0.00%> (-15.00%)	⬇️
.../assets/src/views/userAccounts/PasswordTextbox.vue	61.76% <0.00%> (-8.24%)	⬇️
kolibri/plugins/user/kolibri_plugin.py	83.33% <0.00%> (-7.58%)	⬇️
...ibri/core/assets/src/state/modules/core/actions.js	23.47% <0.00%> (-1.94%)	⬇️
kolibri/core/auth/api.py	86.70% <0.00%> (-1.07%)	⬇️
kolibri/core/device/serializers.py	92.53% <0.00%> (ø)
kolibri/deployment/default/urls.py	93.33% <0.00%> (ø)
kolibri/deployment/default/dev_urls.py	0.00% <0.00%> (ø)
kolibri/core/discovery/utils/filesystem/posix.py	57.28% <0.00%> (ø)
... and 9 more

[indirectlylit]

@mrpau-dev would you mind testing this on Android?

[mrpau-richard]

@indirectlylit I'm having the same issue with the installer built in this PR. The Kolibri Android app crashes after I launch it.

[indirectlylit]

merging to get it in place for integration testing