Use withdrawal address instead of execution address and rework parts around it

[remyroy]

Fixes #133

Changes

• Rework the documentation around the execution address to simplify it and mostly replace it with the withdrawal address term.
• Minor updates to code that still used the execution address term.

Types of changes

What types of changes does your code introduce?

• [ ] Bugfix (a non-breaking change that fixes an issue)
• [ ] New feature (a non-breaking change that adds functionality)
• [ ] Breaking change (a change that causes existing functionality not to work as expected)
• [ ] Optimization
• [x] Refactoring
• [X] Documentation update
• [ ] Build-related changes
• [ ] Other: Description

Testing

Requires testing

• [X] Yes
• [ ] No

If yes, did you write tests?

• [ ] Yes
• [X] No

Documentation

Requires documentation update

• [ ] Yes
• [X] No

Documentation updates are included in this PR.

Requires explanation in Release Notes

• [ ] Yes
• [X] No

If yes, fill in the details here. Remove if not applicable.

[github-actions[bot]]

Test Coverage: Download HTML Report

Name                                                                 Stmts   Miss  Cover
----------------------------------------------------------------------------------------
ethstaker_deposit/__init__.py                                            1      0   100%
ethstaker_deposit/bls_to_execution_change_keystore.py                   33      2    94%
ethstaker_deposit/cli/__init__.py                                        0      0   100%
ethstaker_deposit/cli/existing_mnemonic.py                              28      0   100%
ethstaker_deposit/cli/exit_transaction_keystore.py                      41      2    95%
ethstaker_deposit/cli/exit_transaction_mnemonic.py                      63      8    87%
ethstaker_deposit/cli/generate_bls_to_execution_change.py               59     11    81%
ethstaker_deposit/cli/generate_bls_to_execution_change_keystore.py      42      2    95%
ethstaker_deposit/cli/generate_keys.py                                  41      2    95%
ethstaker_deposit/cli/new_mnemonic.py                                   26      0   100%
ethstaker_deposit/cli/partial_deposit.py                                62      5    92%
ethstaker_deposit/credentials.py                                       197     68    65%
ethstaker_deposit/deposit.py                                            57     10    82%
ethstaker_deposit/exceptions.py                                          2      0   100%
ethstaker_deposit/key_handling/__init__.py                               0      0   100%
ethstaker_deposit/key_handling/key_derivation/__init__.py                0      0   100%
ethstaker_deposit/key_handling/key_derivation/mnemonic.py               90      7    92%
ethstaker_deposit/key_handling/key_derivation/path.py                   17      1    94%
ethstaker_deposit/key_handling/key_derivation/tree.py                   36      0   100%
ethstaker_deposit/key_handling/keystore.py                             100      0   100%
ethstaker_deposit/settings.py                                           26      0   100%
ethstaker_deposit/utils/__init__.py                                      0      0   100%
ethstaker_deposit/utils/ascii_art.py                                     2      0   100%
ethstaker_deposit/utils/click.py                                        72      3    96%
ethstaker_deposit/utils/config.py                                        3      0   100%
ethstaker_deposit/utils/constants.py                                    29      0   100%
ethstaker_deposit/utils/crypto.py                                       29      1    97%
ethstaker_deposit/utils/deposit.py                                       9      0   100%
ethstaker_deposit/utils/exit_transaction.py                             24      0   100%
ethstaker_deposit/utils/file_handling.py                                 8      0   100%
ethstaker_deposit/utils/intl.py                                         54      3    94%
ethstaker_deposit/utils/ssz.py                                          60      7    88%
ethstaker_deposit/utils/validation.py                                  244     52    79%
----------------------------------------------------------------------------------------
TOTAL                                                                 1455    184    87%