Make Beancount functionality a standalone script that uses Spotbit #61

Currently, Spotbit cli can generate a beancount report using the beancount command.

We want the beancount functionality to be made into a standalone app that uses Spotbit for price data.

This can be done in the following steps:

• Add a configuration option for beancounter.py that allows the user to define which remote Spotbit should be used for price data.
• [ ] Add code that allows beancounter.py to read its own dotenv file.
• Remove the beancount command from app.py.