Update check balance

[jmoreira-valory]

A few updates related to checking balance:

• Refactored to a method at the top of the script.
• Checked agent address also on re-runs.
• Displayed always in DAI units.
• Rearranged displayed text for better display.
• Added spinner.

Additionally:

• Added copyright information
• Minor cosmetic changes in the messages displayed

This is how it should look like:

Your agent instance's address: 0x456170dd7ab80901957283776629b8c6B2542E78
Your service's Safe address: 0xb9d8fDF0e1a5bC188fE314a9CbaB2BAb71C5F33e

Please, fund your agent instance's address with at least 0.0500 DAI.
    - Address: 0x3AF1698a2661C57967475F6E9B6f0DC6593284Fa
    - Balance: 0.0504 DAI
      OK.

Please, fund your service Safe's address with at least 0.500 DAI.
    - Address: 0xea6C5047D44388964124C69A8a9926FFfDEe6AF7
    - Balance: 0.4700 DAI
      Waiting... / 
    - Updated balance: 0.5000 DAI
      OK.

Setting up the service...

[jmoreira-valory]

@Adamantios Here I removed the check for the minimum balance of the agent instance address.

[Adamantios]

Why?

[jmoreira-valory]

"Functions should do only one thing":

The method was doing 2 things: conversion and formatting.

Now formatting is done in the strings using this function (I added DAI to these strings).

This allows using the output of this function as a number directly, in case it is ever required.