Fixed #167. Refactor: centralized type handling for simple operations such as add and subtract, and added branch coverage for this

[akerfel]

Created functions which take two Number objects, and either adds, subtracts, or compares them. These Number objects can be of type Integer, Long, Float, Double, BigInteger or BigDecimal. Also added function which does row multiplication for Number arrays.

Instead of using the same code spread over multiple functions, this patch centralizes it to one class (Operations.java), thus decreasing code repetition and cylcomatic complexity, while increasing readability.

Also added branch coverage for these different Number types, since it was missing (previous tests only tested relevant functions using Integers).

For more details, see issue #167.

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