Renamed task directories to simplify Gitlab navigation

Task_C/src/visitor/CountingVariablesVisitor.java

Task_C/src/visitor/EvaluationVisitor.java

Task_C/src/visitor/ExpressionTest.java

Task_C/src/visitor/Minus.java

Task_C/src/visitor/Number.java

Task_C/src/visitor/PrintVisitor.java

Task_C/src/visitor/SimpleExpression.java

Task_C/src/visitor/Sum.java

Task_C/src/visitor/Variable.java

Task_C/src/visitor/Visitor.java

Task_C/src/visitor/VisitorTest.java

Task_C/src/visitor/overview.png

Task_C/src/visitor/overview.ucls