GUI: Add too long string literal warning code to theme generation tool.

This has the same effect as clang's -Woverlength-strings warning of
string literals longer than C++ compilers are specified to work with.
GUI: Add code to default theme generation to reduce string length.

The additional code skips the extraneous spaces after the end of an
XML close brace (>) reducing the string literal by 3106 characters,
thus bringing it within the limit for C++ string literals.

Have regenerated the default.inc from scummclassic with this change.
Merge pull request #384 from digitall/themeMaxSize

Bug fix for default builtin theme exceeding maximum size for C++ string literal..