refactor: turn on strict mode in Typescript configuration

[karrui]

Problem

Turn on strict mode that allows the Typescript compiler to alert us on undefined or nullable errors.

Various changes are made in the codebase to accommodate this change.

Also add better JSDocs on the functions I've come across

Closes #163

Features

• add vendor typings for convict-format-with-validator in types/vendors
• add vendor typing for express-device package in types/vendors
• add vendor typing for bson-ext package in types/vendors

Improvements

• Correct all errors that arise from the change to strict mode

Dev Dependencies

• bump ts-jest from 26.1.4 to 26.3.0: This removes the Typescript unsupported warning
• bump @shelf/jest-mongodb from 1.2.2 to 1.2.3: I thought this would allow us to not have to manually setup and teardown on dbHandler.connect, but that does not seem to be the case. No harm updating though so it stays.

[karrui]

The number of lines is a lie again, most of it is due to adding vendor typings to packages without types!!

[karrui]

I have absolutely no clue why testcafe fails to start....

YAYYYYYYYYYYYYY TESTS PASS

[liangyuanruo]

Thanks for getting this across the finish line; in retrospect strict mode probably should have been enabled at the start. I see plenty of non-null assertions being made, but I'll take what I can get.

[karrui]

Thanks for getting this across the finish line; in retrospect strict mode probably should have been enabled at the start. I see plenty of non-null assertions being made, but I'll take what I can get.

I added lint rules for non null too, they are now warnings so it should get devs to be more aware too

[mantariksh]

I'm working on fixing these merge conflicts, will merge once I'm done