Separate signal attachment between morango core and kolibri sync logic

[bjester]

Summary

• Updates sync command logic to attach to initializing.started signal manually, which itself was hacked to fire manually
• Updates the Kolibri app logic to attach to the initializing.completed signal, which is supported in morango and was the original implementation

References

Closes learningequality/morango#201
#11244

Reviewer guidance

See #11244

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Testing checklist

• 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

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

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

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b5.dev0_git.148.g518eda4c.pex
Windows Installer (EXE)	kolibri-0.16.0b5.dev0+git.148.g518eda4c-unsigned.exe
Debian Package	kolibri_0.16.0b5.dev0+git.148.g518eda4c-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b5.dev0+git.148.g518eda4c-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b5.dev0+git.148.g518eda4c-0.1.0-debug.apk
TAR file	kolibri-0.16.0b5.dev0+git.148.g518eda4c.tar.gz
WHL file	kolibri-0.16.0b5.dev0+git.148.g518eda4c-py2.py3-none-any.whl

[rtibbles]

Code changes look precisely right to me - I hadn't done this previously, as I didn't know if there would be an issue with firing the signals on completed rather than started. Will manually test and approve!

[bjester]

@rtibbles Yes, the change to started was to avoid overlap and it connects with the changes that are indeed needed in Morango, but I'm planning to incorporate that with new flexibility in the Morango clients

[rtibbles]

Manual testing also checks out: