no issue
- Adds validations for imported CSV data
- These checks include obvious validation checks for data - like if email addresses are valid, checking if Stripe configured when entries with stripe_customer_id are present and additional server-side validation for entries with stripe_customer_id to check if they appear in connected Stripe account
- The validation set is calculated by naive choosing of first 5, middle 5 and 5 tail records from imported set. This logic comes from observations that errors usually apear withing "test" records in the beggining or the end of the file. These selection rules might change in the future if we find a need for it.
- Adds papaparse CSV parser, which was chosen for it's maturity and relatively small minified size. In the future this library should be lazy-loaded to make the first page load UX nicer
