This is needed for implementing reliable serialization of custom translations. As long as they are merely ints they cannot be restored on loading a savegame because the serialization code does not know that these variables are special.
This eliminates nearly all palette dependencies, most importantly font translation will now be done on True Color data, making translations on True Color font less destructive.
* removed refreshFreq variable and related code. This only got into the backend because of stupid interpolation code in some of the Build games which has long been removed.
* save FixedBitArrays as base64 in savegames.
* allow indirections in the string table - by prefixing the language string with '$$' the remaining text is interpreted as another string label to resolve.
* constexpr in palette code, also replacing #defines with enums.
* removed unneeded includes
* moved global brightmap to GPalette
* took Build tile init code out of the FTextureManager class, because this code is not compatible with how real Build games need to go about it, making the texture manager not shareable.
* removed dependency on higher level info from the Image class.
