Cleanup ctkUtilsTests using QTestLib

Issue #348
Add support for min, max, inf and NaN in ctkUtils

Closes #348
Add support for inf and nan in ctkRangeWidget

Issue #348
Reject inf single step in ctkRangeWidget
Merge branch '348-order-of-magnitude-infinite-loop'

* 348-order-of-magnitude-infinite-loop:
  Reject inf single step in ctkRangeWidget
  Add support for inf and nan in ctkRangeWidget
  Add support for min, max, inf and NaN in ctkUtils
  Cleanup ctkUtilsTests using QTestLib