Use a file in case we need further configuration e.g. open_with

Each of the docker wrappers (app-docker, cli-docker, etc)
can make use of this single script in order to integrate
the various actions that they would like to perform.

In most cases, `. "$(dirname "$0")/docker app"` should
suffice as the entirety of script. With time, these scripts
might should be deprecated.

In travis, the `.omero/app-docker` invocations should still
work, but `.omero/docker app scripts`, for example, should
be usable for a multi-staged build.

To test what the script would do, use:

```
  ACTION=echo .omero/docker app scripts
```

lib-docker depends on having a local phase.
Now, the run function can take a first argument
of `--local` to perform actions outside of docker.

Some docker commands need to be called with
`-u $USER` as defined in each stage. This flag
now permits to swap away from `-u root`.