Refactor: Create strongly typed class for options handling

[rchl]

• Create strongly-typed dedicated class for handling settings
• Remove support for deprecated settings starting with trailing_spaces_
• Switch to 3.8 runtime for types support (related: https://github.com/wbond/package_control_channel/pull/8771)
• Remove dependency on sublime_lib (require for 3.8 runtime)

Apart from the changes listed above it should introduce no behavior changes (not fixing known bugs even, that will come later).