Change how execution time is presented. Minor refactoring

src/main/java/algorithmcomparison/Bubblesort.java

src/main/java/algorithmcomparison/Heapsort.java

src/main/java/algorithmcomparison/Insertionsort.java

src/main/java/algorithmcomparison/Main.java

src/main/java/algorithmcomparison/Mergesort.java

src/main/java/algorithmcomparison/Quicksort.java