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

As Clang has given a warning for, the default.inc file string literal is currently exceeding the maximum size for a C++ string literal and thus the behaviour of this is compiler dependent :/

This may explain some issues seen with the built in theme in the past.

To remove this issue currently, I have amended the scummtheme.py tool to reduce an extraneous space after the XML tag close bracket in the default.inc format generation. I have tested this and ScummVM still compiles and parses the builtin theme perfectly well with this change, but this removes over 3000 characters from the string bringing it below the limit.

To avoid this in future, I have also added code to the tool to give a warning if the string literal exceeds the maximum length again.