The biggest hold-up was missing fields (`premium_tier`,
`welcome_screen`, etc.) but it looks like someone has provided a
helpful function called `createGuild(...)` to provide sensible default
values.

This commit fixes the errors related to creating a guild from a
template. I've also refactored the code to include roles and channels in
the template.

To make sure that the @everyone role is cloned correctly, when
creating the guild from a template, we check if the role's ID
matches the template's `source_guild_id`. If it does, we set the
@everyone role to the new guild's ID.

I think we'll need to discuss the proper way to provide default values
here. `premium_tier` for example should never be provided from the
template so it's fine going after the spread operator.

This commit still doesn't allow guilds to be created from template
because the next error is that `welcome_screen` doesn't exist. Our
options:

1. Provide default values in the ORM
2. Provide default values in the guild creation process
3. Throw an error if the template is missing values

Resolves: #1283 but creates a new issue

`Promise.all(...)` runs these simultaneously, yet role depends on the
guild to be created first. This can lead to a race condition. I've
awaited role creation too because the call to `Member.addToGuild(...)`
relies on the role to be created.

* Add eslint, switch to lint-staged for precommit

* Fix all ESLint errors

* Update GH workflow to check prettier and eslint

* Add script to automatically add license to each file

* Add license preamble to each file.

* Fix existing preamble detection breaking due to line endings. Git :(

* Prevent license from being added to code with other licenses