core: Added LexoNumericComparator utility

This utility helps to sort strings which include numeric subsequences
according to sensible ordering - sorting numeric subsequences
numerically, and the rest lexicographically.

A corresponding test class is added.

Change-Id: I8c68446ea6f1865a51455a0a359df339bfb15bba
Signed-off-by: Lior Vernia <lvernia@redhat.com>