Refactor use of RifReaderSettings

[magnesj]

Refactor RifReaderSettings, separate the data structure sent to reader from the data structure in preferences. See RifReaderSettings::createGridOnlyReaderSettings() for the only use of importSummaryData flag.

Avoid setting the preference structure to default nullptr and avoid the confusing fallback to the structure in Preferences in RifReaderInterface::readerSettings()