Add options for processing SGF files

[herzbube]

With the integration of SgfcKit the project now has full control over how to load and save SGF files. Expose some of the large number of processing options offered by the underlying SGFC in the app's UI.

[herzbube]

Preliminary ideas:

• Encoding mode when reading
  • Only -E1 = Default
  • Only -E2
  • -E1 and -E2
  • Note: -E3 must not be offered because the marshaling of string data between libsgfc++ and SgfcKit always uses UTF-8. In fact -E3 will likely be removed from SgfcKit because of this.
• When to allow an .sgf to be processed?
  • Only with no warnings and errors
  • With non-critical warnings and errors (default)
    • Paradoxically errors are generally less bad than critical warnings. An error is often fixable in some way or other by SGFC. Example: A property that requires a value but has none (empty [] in the SGF content) generates error 17, SGFC removes the offending property which generally results in SGF content that is then processable.
  • With critical or non-critical warnings and errors (NOT RECOMMENDED)
• List SGFC non-critical warnings and errors to be ignored
  • This list is passed directly to SGFC option -d
  • Prepare a careful selection of default warnings and errors
  • Besides reducing noise, this can be useful if the user wants to use the "Only with no warnings and errors" processing option.

[herzbube]

Always use the following arguments:

• SGFCArgumentTypeDeleteEmptyNodes. Because of this we should also add SGFCMessageIDEmptyNodeDeleted to the list of warnings that we ignore.

Expose the following arguments in addition to the stuff from the previous comment:

• SGFCArgumentTypeDisableWarningMessages: Useful instead of silencing individual message IDs.
• SGFCArgumentTypeEnableRestrictiveChecking: Adventurous souls might find this interesting.
• SGFCArgumentTypeReverseVariationOrdering: Because Little Go only reads the main variation this option might be important.
• DefaultEncoding: Another option that might be important in order to be able to read files. Since iconv does not offer a function that lists the encodings supported on that particular system, the user will have to enter the encoding name in free form. Validation of the entered encoding name is possible by executing iconv_open() and specifying the encoding as the "fromcode" parameter (SGFC always uses UTF-8 for the "tocode" parameter).
• ForcedEncoding: Ditto

The following messages should be ignored by default:

• SGFCMessageIDEmptyValueDeleted: The SGFC docs for -d suggest this as a possible non-critical message that could be safely ignored.
• SGFCMessageIDPropertyNotDefinedInFF: Ditto
• SGFCMessageIDEmptyNodeDeleted (this is generated only if SGFCArgumentTypeDeleteEmptyNodes is used)
• SGFCMessageIDGameIsNotGo: We simply ignore such games. This is a critical warning.
• SGFCMessageIDMoreThanOneGameTree: We list all game trees, so notifying the user about this is not necessary. This is generated only if SGFCArgumentTypeEnableRestrictiveChecking is used.

[herzbube]

Simplified settings:

• Paranoid
  • Allow processing only with no warnings and errors
  • SGFCArgumentTypeEnableRestrictiveChecking
  • No messages disabled (even remove the messages on the default ignore list)
• Sensible default
  • Allow processing with non-critical warnings and errors
  • Some messages are in the default ignore list
• Ignorance is bliss
  • Allow processing with critical or non-critical warnings and errors
  • SGFCArgumentTypeDisableWarningMessages

Can the encoding options also be incorporated?