Added version's qualifier normalization
* From the qualifier are removed characters 'v' and '-' in order to
compare properly timestamps

* Fixed usage information
[maven-release-plugin] prepare release plugin-cleaner-0.2.1
[maven-release-plugin] prepare for next development iteration
Introduces a new command line param ``--mode`` that allows to resolve
duplicates based on the following options:

* ``dropinsOnly`` (default) - Preserver the Eclipse's plugins and remove
duplicates only from the dropin folder

* ``prefereDropins`` - If there are multiple version of the bundle with
the same version, remeve duplicates from dropins folder.

* ``unlimited`` - Collect all possible plugins and remove duplicates
regardless their location.

Improved documentation.
Merge branch 'master' into staging
Introduced release launching with a dry run