Allow copy operations to suppress layouts.

Added support for the [suppressLayouts](http://www.jfrog.com/confluence/display/RTF/Artifactory+REST+API#ArtifactoryRESTAPI-CopyItem) parameter which allows copying to arbitrary locations instead of trying to map artifacts to a layout.

For example, if you want to copy a number of artifacts from a maven repository to a new repository which only serves a flat listing of jar files from different organizations or modules this parameter is required.

* Please use boolean values.
* Also please add a docstring, explaining what is suppress_layouts. E.g. list a short example and say what will happen when this flag is set, and also when it isn't.

This flag is not documented in the Artifactory source, so we better be explicit here.