refactor: Theme & ThemeOptions

- Makes the naming more consistent between the two (needs another check)
- Re-order types to be defined in the same order in each module
- Fixes the breakpoints function types on the theme
- Removes the now unnecessary runtime overhead of ThemeHelpers.addBreakpoint
- Add ThemeHelpers.addBreakpointDown function
- Add ExampleTheme.res file to the repo

Author: illusionalsagacity