Move MathExtra back to lara-framework after .code is a global attribute

[joaobispo]

          That is true. The move was done since Clava was the only Weaver that actually supported this API, I assumed it was the only one where it would be used.

As for adding .code as an attribute of the base joinpoint type (LaraJoinPoint), I agree. I had planned for us to have a discussion about this in the near future.

Originally posted by @lm-sousa in #41 (comment)