Merge generated code instead of overwriting it

[wegendt-bosch]

If users modify the generated C code they can no longer use Mita as that would overwrite their changes. Our goal however, is to provide a jump-start for C development should the user choose to do so. Thus, we need to introduce means to merge the user-made changes and the code we're generating.

We could use the TextStreamMerger of the team plugin to perform the merge of newly generated files. If the merge fails, the code generation fails or we bring up a merge dialog (difficult if we ever introduce command line tooling).