Changed tool version matching + minor changes
- GalaxyToolMetadataParser and GalaxyWorkflowStep: assume an empty tool version matches any specific version.
- added the concatenation tool files and updated the tool_conf.xml file.
- added a short description on how to add tools to the test data in this project: adding-tools.txt.
- changed the link for the Apache License version 2.0 from http://opensource.org/licenses/Apache-2.0 to http://www.apache.org/licenses/LICENSE-2.0.html.