Document project coding standards

[sebbrudzinski]

Lately, we have integrated the checkstyle plugin with the Ant build. The checkstyle plugin is responsible for verifying and enforcing coding standards in the project. The checkstyle rules are heavily based on the Java coding conventions by Oracle. It's a good time to prepare a wiki page, that lists at least some of the most important rules, that are often broken in the new pull requests (braces placement, unusued imports, modifiers order, etc.) All the rules we use are under the project directory, in the checkstyle.xml file (it only contains name, but it's easy to find the meaning on the Checkstyle website)