Fix slot leak

[bigopon]

Fixes aurelia/templating-resources/issues/392

Thanks to @thomas-darling for this fix.

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Currently, ShadowSlot keeps track of what Node has been projected through it, via an internal children array but it doesn't untrack(remove) those tracked Node from the array when the owning views of those Nodes get removed. Fix this by removing them in ShadowSlot.prototype.removeView and ShadowSlot.prototype.removeAll

Also revamp testing setup so that it can remove the usage of jspm for testing, while keeping the build process intact. Now we have:

npm run test
npm run test:watch
npm run test:debugger

with an option to go full integration tests to have more solid infra for tricky parth such as Shadow DOM emulation.

@EisenbergEffect @fkleuver @StrahilKazlachev

[claassistantio]

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2 out of 3 committers have signed the CLA.

✅ baerrach
✅ bigopon
❌ AureliaEffect
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[bigopon]

@fkleuver @EisenbergEffect @StrahilKazlachev ready for review

[StrahilKazlachev]

@bigopon I've not been active for some time, so are dist files added now with the PRs?

[bigopon]

@StrahilKazlachev its because the target branch is develop and the pr is based on master. The commits that contain those dist should ideally ve in develop already. Cc @fkleuver

[bigopon]

resolved by #678