admin panel: db, models, routes

[Nalipp]

create seed data with existing data model in data.sql
connect basic endpoints to react admin panel

[stephaniesimms]

• seed data for users, charges, salaries
• script to seed db
• tests
• user model: find, update, delete (auth @emitamago @mvatanya)
• user routes: get, post, patch, delete
• salaries model: find all, update, delete
• salaries routes: get, post, patch, delete
• charges model: find all, update, delete
• charges routes: get, post, patch, delete

[stephaniesimms]

all tasks completed as part of related issue #29
charges model, routes, tests are part of new issue #39