[ESLINT] audit rule: id-length

[kieckhafer]

We have multiple eslint warnings for the id-length rule.

This ticket is to:

1. Fix all these eslint warnings. This SHOULD mean actually fixing them, but could also mean adding an eslint-disable-line, if applicable.
2. Change the id-length rule from a warning to an error so we do not introduce new warnings in the future.

As the purpose of this rule is to make sure variable names easily provide context, I propose we add one, maybe two exceptions of short var names that the context is usually a given:

• i: well known to represent an incrementer.
• e: I could understand this one going either as error or event, so if the consensus is don't allow e, that's fine

https://eslint.org/docs/2.0.0/rules/id-length#options

[kieckhafer]

Closed via #5298