Move static IOMarket methods to namespace

[ramon-bernardo]

Pull Request Prelude

• I have followed proper The Forgotten Server code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

• Bring closure to the IOMarket class and its static instance by moving it to a namespace.

IOMarket::x to tfs::io::market::x

[ramon-bernardo]

tfs::db::market it's more readable?