* Use ScriptValueP for all Value types.
  All Value types now inherit from AnyValue, all Fields inherit from AnyField.
  Common properties, in particular scripting, are done by AnyValue/AnyField

* Repurposed ImageValueToImage as the representation for image values.

* Added LocalSymbolFile as the representation for symbol values.

* Moved FileName to package.hpp, and renamed it to LocalFileName.
  The notification of packages that was previously done by Reader/Writer is now done by LocalFileName.

* Added toFriendlyString to ScriptValue, it is used (primarily) for the card list.
  The idea is that this function strips tags and always returns something, for example "<image>" for images.

* Removed backwards compatibility with 0.2.7 style tags, since I was too lazy to update it.

Code is a bit messy right now, since cleanup will come in separate commits.