Add support for Nuxeo SDK in tomcat distributions

Nuxeo tomcat distribution should provide some helper files for Nuxeo IDE:
1. a distribution.properties file which indicate the name / version of the SDK (i.e. distribution)
2. an artifact.properties file which list the JARs that comes with the distribution and their bindings on maven artifacts.
The key should be the JAR file name (without the path) and the value a maven GAV. Example:

EditableImage-0.9.5.jar=net.java.dev.mistral:EditableImage:0.9.5
JAI-Adapter-0.9.5.jar=net.java.dev.mistral:JAI-Adapter:0.9.5
Operations-0.9.5.jar=net.java.dev.mistral:Operations:0.9.5
activation-1.1.jar=javax.activation:activation:1.1
ant-1.7.0.jar=org.apache.ant:ant:1.7.0
ant-launcher-1.7.0.jar=org.apache.ant:ant-launcher:1.7.0
...

The directory to store that files is currently nxserver/sdk.
You may change its location if needed.

Also we will need Nuxeo test dependencies.
You can either include these dependencies in sdk/sources directory, either (to avoid putting more JARs in the distribution) to add a test-artifact.properties file that includes only test JARs mapping.
This way on the Nuxeo IDE we can download test JARs when installing an SDK. (and copy them in sdk/tests)