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

package.json

@@ -49,8 +49,9 @@
     "babel-eslint": "^7.1.1",
     "babel-plugin-syntax-flow": "6.18.0",
     "babel-plugin-transform-flow-strip-types": "6.22.0",
+    "babel-preset-env": "1.6.0",
     "babel-preset-es2015": "6.24.1",
-    "babel-preset-stage-0": "6.24.1",
+    "babel-preset-stage-3": "6.24.1",
     "babel-register": "6.26.0",
     "bcrypt-nodejs": "0.0.3",
     "cross-env": "5.0.2",