Finding areas that are untested and need love (#4131)

* Makes InstallationRouter like others

* Adds testing for Range file requests

- Fixes issue with small requests (0-2)

* Revert "Makes InstallationRouter like others"

This reverts commit e2d2a16ebf2757db6138c7b5b33c97c56c69ead6.

* Better handling of errors in FilesRouter

* Fix incorrectness in range requests

* Better/simpler logic

* Only on mongo at it requires Gridstore

* Open file streaming to all adapters supporting it

* Improves coverage of parsers

* Ensures depreciation warning is effective

* Removes unused function

* de-duplicate logic

* Removes necessity of overriding req.params.className on subclasses routers

* Use babel-preset-env to ensure min-version compatible code

* removes dead code

* Leverage indexes in order to infer which field is duplicated upon signup

- A note mentioned that it would be possible to leverage using the indexes on username/email to infer which is duplicated

* Small nit

* Better template to match column name

* Restores original implementation for safety

* nits

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -79,10 +79,6 @@ export default class MongoCollection {
     return this._mongoCollection.updateMany(query, update);
   }
 
-  deleteOne(query) {
-    return this._mongoCollection.deleteOne(query);
-  }
-
   deleteMany(query) {
     return this._mongoCollection.deleteMany(query);
   }