General usage instructions
A lot of sites (like codeforces.com, codechef.com) expect only one file as solution source and ignore traditionally for Java language class/package structure. So we need to integrate all non-standard dependencies (often utility-classes) to one file.
This plugin (when you click magic button) analyzes active file, places (replaces) class Main at default package of current module, copies public class from active file to it, copies all dependent classes those can be found in current project and eliminates unused fields/methods/nested classes. Be careful and don't use classes with the same short names in dependencies or in default package - there are possible conflicts, because package info will be lost during preparing Main class.