simplify includes in strings

alib2data/src/XmlApi.cpp

alib2data/src/object/ObjectBase.h

alib2data/src/string/CyclicString.h

alib2data/src/string/Epsilon.h

alib2data/src/string/LinearString.h

alib2data/src/string/String.cpp

alib2data/src/string/String.h

alib2data/src/string/StringAlphabetGetter.cpp

alib2data/src/string/StringAlphabetGetter.h

alib2data/src/string/StringFeatures.h

alib2data/src/string/StringFromStringLexer.h

alib2data/src/string/StringFromStringParser.h

alib2data/src/string/StringFromXMLParser.cpp

alib2data/src/string/StringFromXMLParser.h

alib2data/src/string/StringToXMLComposer.cpp

alib2data/src/string/StringToXMLComposer.h