Noticket: Implement additional path validations for Factorio Manager:

- Added test for instance directories, new backup directories, backup
directories, and import sources.
- Refactored commands to use the new path validations.
- Updated some comments and formatting.

Noticket: Introduce dedicated function for picking Factorio version in Factorio Manager:

- Function is generic, and lets user pick the version more simply with
pre-defined defaults.
- Use the new function in "create" command.

Noticket: Introduce mechanism for validating common paths:

- Add support for validating game installations directory and new
instance directory.

Noticket: Clean-up set-game-dir command in Factorio Manager:

- Small refactoring and fixing of variable names and outputs.

Noticket: Refactor validation of server settings in Factorio Manager:

- Introduce dedicated validation function.
- Drop some unused variables.
- Validate settings while they are being prepared for the JSON file.

Noticket: Drop warning_prompt and bold_* functions:

- Introduce new function that handles promting for dangerous
operations and aborts if user does not confirm operation.
- Replace use of bold_* functions with colorecho function.
- Refactor colorecho and colorprintf to share associative array with
colors, and also support bold variants.
- Write documentation for the colorecho and colorprintf functions.

Noticket: Put a space around backup names in Factorio Manager when listing them:

- Makes it easier to copy/paste the backup name.

Noticket: Make Factorio Manager more robust by requesting all variables to be defined before use:

- Added missing server setting for port.

Noticket: Improve factorio_manager.sh server settings prompt handling:

- Use dedicated functions for colored output (colorecho and
colorprintf).
- Update function documentation to be a clearer.
- Declare all local variables correctly.
- Fix invalid setting type for
ignore_player_limit_for_returning_players.
- Validate user's input (should validate all settings even if user has
not changed them, but not implemented yet).