[STYLE] add ESLint and prettier

[surchs]

This adds:

• ESLint as a code linter
• vue specific ESLint rules and the corresponding plugins
• config for ESLint and ignore file
• prettier as a code formatter
• dependencies for all of this, plus dependencies for editorconfig (needs npm install in vscode to work)

This is related to what we discussed in #74.
I think there is a tradeoff between having something going now and immediately adopting a very strict style guide. I prepared some rules that I think would make sense to adopt eventually (e.g. airbnb style guide) but commented out for now. There are no linting checks to run the code, so all linting warning and errors can be ignored for now.

[surchs]

@jarmoza as we had discussed on slack and #76, I'll merge this so we can use the linter in the open PRs