Refactored math expression reduction.

...cs/gitlab/maikov/exceptions/ImpossibleStateException.java

.../cs/gitlab/maikov/exceptions/InvalidOperandException.java

...ava/ee/ut/cs/gitlab/maikov/expressions/AbsoluteValue.java

...ain/java/ee/ut/cs/gitlab/maikov/expressions/Addition.java

...ain/java/ee/ut/cs/gitlab/maikov/expressions/Division.java

src/main/java/ee/ut/cs/gitlab/maikov/expressions/MathOp.java

.../java/ee/ut/cs/gitlab/maikov/expressions/MatrixValue.java

...va/ee/ut/cs/gitlab/maikov/expressions/Multiplication.java

src/main/java/ee/ut/cs/gitlab/maikov/expressions/Number.java

.../java/ee/ut/cs/gitlab/maikov/expressions/Subtraction.java

src/main/java/ee/ut/cs/gitlab/maikov/expressions/Value.java

src/test/java/ExpressionTest.java