[JENKINS-17680] Show warnings when upgraded from Copy Artifact < 1.26.

When updated from Copy Artifact < 1.26, "Project name" filed gets empty in project configuration pages.
This breaks existing projects using Copy Artifact.

This patch does followings:
* Fills "Project name" with a value configured in old version.
* Prompt a message if  filled "Project name" contains "/", that is, it may have to be split into "Parameter filtetrs".

See attached image for a warning message sample:
![migration_warnings](https://f.cloud.github.com/assets/3115961/658408/67a8a858-d5df-11e2-92bf-d4f17c739805.png)