Major update of TraceFileStatisticAnalyzer

- TraceFileStatisticAnalyzer should ideally contain only trace-file parsing logic (possible rename to TraceFileParser)
- new class TraceTask was created, which contains all the data and all the logic for statistical analysis
- TraceFileStatisticAnalyzer (actually, TraceTask) now returns average response time for all instances instead for finished instances (this can be changed easily in TraceTask)
- TraceTaskTest.java - first JUnit test in this project!