Warn about creating BigDecimal from float or double

Ported from scapegoat, gives a warning when calling BigDecimal.apply(float | double) or instanciating with new. Covers both the Scala and the Java BigDecimal.
It's somewhat cleaner to go through symbols than `toString`. You can access the symbol table using `definitions`, something similar to [this](https://github.com/dragos/scala-abide/blob/rule/iteration-mutation/rules/core/src/main/scala/com/typesafe/abide/core/MutateInsideIteration.scala#L30).