Add setting for naming of include guards

Add a setting that specifies how include guards should be named when using the wizard to generate a new class or header file. This could be some sort of template with a default value like:

%HEADERNAMEWITHOUTEXTENSION%_%EXTENSION%

For a file called "myheader.h" this would generate "MYHEADER_H".
If I modify the setting to:

MYPREFIX_%HEADERNAMEWITHOUTEXTENSION%_%EXTENSION%

Then this would result in "MYPREFIX_MYHEADER_H" for the same header file.

It would be preferable to have this as a per-project setting.