Translations of parsers error messages

[slafayIGN]

Messages from the parsers are in english.

For instance : https://github.com/geostyler/geostyler-sld-parser/blob/master/src/SldStyleParser.ts#L976

   throw new Error('MarkSymbolizer cannot be parsed. Unsupported WellKnownName.');

These messages sometimes have to be displayed for the end user who may be using a UI in another language. It would be great to make the parsers more multilingual.

In addition, the message may contain the "Unsupported WellKnownName". (see #924)

[ocruze]

Done in #928