Prima versione delle API

Checklist

[] Login
[] Signup
[] Update JWT
[] Get User Data
[] Get user contracts
[] Get contracts details
[] Set user permission to contract
[] Change User Data
[] Get possible electricity contracts (for new contracts)
[] New contract electricity
[] Get user electricity usage
[] Get user electricity bill
[] Get possible gas contracts (for new contracts)
[] New contract Gas
[] Get user gas usage
[] Get user gas bill