Add code style formatting settings to the project

[ggalmazor]

This issue should be addressed after closing #171

Software and hardware versions

Any

Problem description

All the code in Aggregate should follow the same code style formatting rules to prevent having superfluous differences while merging contributions.

There should be some clear rules about indentation (size, tabs/spaces, etc.) and other style concerns regarding Java, XML, etc.

After applying this rules with automatic reformatting tools, the resulting code should pass any checkstyle rules defines in the project.

Steps to reproduce the problem

N/A

Expected behavior

N/A

Other information

IntelliJ can export the code style settings used to automatically format the code in a JAR file that contributors can import into their IDE.

There is also a standard cross-IDE tool for defining simple basic rules that: EditorConfig