Add support for greek and cyrillic chars such that it is not

Add support for greek and cyrillic chars such that it is not
necessary to mark them in the proper language for typesetting.

	* src/Paragraph.cpp
	(Paragraph::Pimpl::knownLangChars): new method.
	(Paragraph::Pimpl::simpleTeXSpecialChars): output proper
	latex code for greek and cyrillic chars.

	* src/LaTeXFeatures.cpp: add textgreek and textcyr features.

	* src/Encoding.{cpp,h}
	(Encodings::isKnownLangChar): new method.

	* lib/unicodesymbols: add greek and cyrillic alphabetic chars.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@20931 a592a061-630c-0410-9148-cb99ea01b6c8