OGM-454 Moving internal types to "impl" packages
OGM-454 Moving SPI types to "spi" packages
OGM-454 Moving OptionConfigurator to API package
OGM-454 Avoiding FQNs in JavaDocs of public types
OGM-454 Marking GridType and GridDialect#overrideType() with @Experimental
OGM-454 Extracting interface from class ConfigurationContext to avoid leaking impl types on SPI contracts

* Also moving context base classes to "spi" as they are intended for usage in dialect modules
OGM-454 Splitting up ConfigurationPropertyReader into SPI and implementation part to avoid references from dialects to internal classes