BUG-1051: logback configuration loader proposal

- uses environment variable logback.config.d (pointing to config root folder)
- removes previously loaded logging configuration
- applies all config files from config root folder in alphabetical order
- requires:
  - to be added to osgi.bundles (configuration.ini)
  - existing logback.config.d variable (configuration.ini)
  - logback config files in specified config root folder
- added overloads for load method
- enriched util class protection against "accidental" instantiation
- using precompiled pattern while iterating folder content
- added classcast protection for case when the logging backend differs from logback

Change-Id: Id0242c78fe39b9631d1a4bca66d9674f7a3fec62
Signed-off-by: Michal Rehak <mirehak@cisco.com>
Merge "BUG-1051: logback configuration loader proposal"