Name already in use

Add functionality to allow an environment variable to indicate that the
COmanage database schema should be updated (./Console/cake database).
This is helpful when deploying a new version of the code that does not
result in a change in the version number and so upgradeVersion does not
fire. An example of this scenario is when new code is introduced in the
develop branch but before a release happens.

Also add functionality to allow an environment variable to indicate that
a non-core plugin should be enabled.

Because some deployers will mount or inject their own mapping between
the _shibd user and its UID the entry point script should execute the
proper chown command to make sure that at runtime necessary files and
directories have the correct ownership.

Also emit a WARNING if any files in /etc/shibboleth are not readable by
the _shibd user.

Moved the registry build and all COmanage specific
environment varilables later in the Dockerfile template
so that more layers can be reused when changing
COmanage registry versions.

Changed layout so that /local is a symlink to
/srv/comanage-registry/local instead of the other way
around so that plugins can easily reference files under
/srv/comanage-registry/app such as the StandardController
view files add.ctp and edit.ctp.

Better Docker stack documentation and removed old documentation
for compose and stacks.

SHIBBOLETH_SP_METADATA_PROVIDER_XML may still be injected
using the _FILE approach but it is handled uniquely now
to prevent an error message from the bash declare
command caused by the contents of the file usually containing
special characters. Fundamentally this is caused by the
left and right-hand sides of

declare "${config_var}"=`cat $file_name`

being evaluated before the actual 'declare' command is evaluated.

The ServerName for Apache HTTP Server may now be injected
using the environment variable SERVER_NAME. If not injected
then the entrypoint scripts will attempt to determine the
value for ServerName from the X.509 certificate for HTTPS.

Since the Apache version used in the images is recent enough
that SSLCertificateChainFile is obsoleted removed the ability
to inject an explicit chain file and updated the documentation to
note that the intermediate CA signing certificates should be
included with the server certificate sorted from leaf to root.