Fix: Fee token and Account improvements

[tabaktoni]

Development related changes

Restructure fee_token and account

• created Accounts class for dealing with accounts
• cleaned state
• OOP improvement for fee_token extracted from the wrapper
• OOP improvement for account extracted from the wrapper
• wrapper 'starknet' made public accessible

Not perfect (as starknet_wrapper is now a constructor parameter) but I think it has good direction.
Now both fee_token and account have similar structure and implementation.

Checklist:

• No linter errors
• Performed a self-review of the code
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Linked the issues which this PR resolves
• Updated the tests
• All tests are passing