added single eunit test run capability;
refactored runconfig-related classes; modified eunit runconfig (added option which allows to run tests on selected functions or selected modules);
added 'rerun failed tests' action;
added 'run selected test files' capability; added tests for it;
added Rebar Eunit tests run configuration (with capability to run single or multiple tests and/or test suites);
fixed navigation from tests results to code; cleaned up code;