Revert "common: rename App to ImageName"
Revert "common: rename App to ImageName"

We need to revert this commit again so rkt can be vendored with a
version of docker2aci with the converting ports feature *but* compatible
with appc 0.5.2.

This reverts commit f4ca82c1e2de3d4edd554ed878576b593fe2bb0f.

OMWAVE/docker2aci,dgonyeo/docker2aci,appc/docker2aci,dgonyeo/docker2aci,jsoriano/docker2aci,ChengTiesheng/docker2aci,appc/docker2aci,jsoriano/docker2aci,jonboulle/docker2aci,iaguis/docker2aci,jumpstarter-io/docker2aci,vishvananda/docker2aci,mclarkson/docker2aci,pquerna/docker2aci,OMWAVE/docker2aci,vishvananda/docker2aci