Rework config and config loading

[redmie]

Commit description:

• Remove config crate for a manual toml config loading scheme
• Structure config via several rust struct (keep it simple: removed the ability to create users or set specific database names, can still be easily coded again if needed)
• Add a --defaults arguments to see internal defaults
• Do not load configuration file by default, use internal defaults
• Clean up main.rs by spliting content between main.rs and server.rs
• Rename parse.rs to parse_args.rs and move functions around.
• Add configuration as data accessible when needed from an actix request
• Update README.md to reflect changes affecting the setup process

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I had some personal problems so it took a bit more time than planed. We stop writing config to file when it does not exist (which is bad practice) but just use internal defaults. Configuration is now more structured ! Please review the changes @dobefore

[dobefore]

It's OK! And thanks for the code organization.It looks well-structured and clean!