Fix ES limiting nested results to 3

ElasticSearch limits the size of nested queries to three to prevent some lag. This adds a Django setting passed to each query template to set the inner_hits.size property.

Also includes a REST framework-esque refactoring of the search API views and better unit tests.

100th merge request!

changed the description

added 2 commits

• 1abc19b7 - Refactor search APIs
• 5f5920f8 - Rewrite search unit tests

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changed the description

added 1 commit

• fab6a359 - Move SearchAPIMixin to arkindex.project.mixins

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added 6 commits

• fab6a359...6121c0a1 - 2 commits from branch master
• 80b7fd08 - Add a setting for ES nested results size
• 83e2625e - Refactor search APIs
• 18179600 - Rewrite search unit tests
• b592b444 - Move SearchAPIMixin to arkindex.project.mixins

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added 1 commit

• 750c83e0 - Show transcriptions count in act search

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merged

mentioned in commit 94fd57ba