- preparation for moving the base class out of Ghost
- refactored so that all the logic for file loading and fallbacks live in the base class
- theme i18n now only overrides init with the properties it needs, filepath generation and error handling
- this makes it much easier to move the i18n file out, and eventually have theme i18n live elsewhere too
- also prepares for using DI for logging
- the core i18n library and theme i18n library have slightly different methods of getting a candidate string
- both of them use forms of jsonpath, meaning they both require jsonpath as a dependency
- to try to get to a point of being able to rip more things out of ghost, we want to have less dependencies
- so instead of overloading the method, we pass in a stringMode as an argument
- eventually we might not need an overloaded class for themeI18n at all, which would simplify the codebase
- preparation for using DI instead of requires, so we can move this out of Ghost
- have done this for both the main i18n and theme i18n file
- refactored the constructor
