enh: Delete Application and its shares

[enjeck]

Fixes #991

[enjeck]

Need to check/fix some edge cases:

• [x] Delete shares from a newly-created context without reload
• [x] Delete shares from a context whose shares were updated
• [x] check that transfer context works. Not related to this, but caught a bug https://github.com/nextcloud/tables/issues/1046
• [x] check that shared resources are removed when context is deleted

[enjeck]

@blizzz How can I fix the Static Analysis errors here?

[blizzz]

@blizzz How can I fix the Static Analysis errors here?

Ah, leftovers from my changes. I added a parameter to ContextService, but changed name and type during working on it. Alas not everywhere. So it's fixing, fix-upping the original commit, and rebasing with squashing it.

[blizzz]

Done and rebased.

[juliushaertl]

/backport to stable0.7

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