Format code using clang-format

[Calinou]

We should look at using clang-format to format code automatically. This will lead to a more consistent code style overall.

If clang-format has a preset commonly used for Qt applications, we could use that one.

[azagaya]

Yes, we already discussed that on discord! Also we discussed about defining a case style. Right now in changing all the text in code to english, because it was in spanish and other potential contributors complained about that. Next i will make a commit with clang-format applied to all the files, and then write a document with the casing style. Right now there is a mix of everything.

[azagaya]

All files were formated with clang-format, and contribution details added to CONTRIBUTING.md.