Jgitproxysshkeyreadme

- replace scm by jgit on UpdateApplicationMojo and remove FileSet usage from this mojo
- add a way to set HTTP Proxy for jGit ssh session (ssh over http proxy : paas instance behind proxy)
- add targets : sshkeylist, sshkeyadd, sshkeycheck and add "available targets" readme section 
- add very first Integration Tests and unit tests