Add APISpark extension

[jlouvel]

This extension should be able to:

• introspect a web API contract (like the WADL and Swagger extension) for both Restlet API and JAX-RS API based code
• send it to an APISpark (https://apispark.com/) web API cell using its meta-API
• include the client SDK to interact with APISpark

workload: ? (the extension has already been added, I'm not sure what need to be done).

[quilicicf]

A preview will be available in APISpark v2.1 that will be able to:

• introspect an RF web API contract
• inject it into an APISpark web API contract cell

[jlouvel]

Assigned to @thboileau to complete the Introspector (logs, metadata, etc.)
#workload: 2h