Make APEX install optional

[martindsouza]

Based on this http://joelkallman.blogspot.ca/2016/03/an-important-change-coming-for-oracle.html APEX will no longer be installed by default. Either make it a requirement or conditionally compile objects.

[martindsouza]

When APEX does not exists, oos_util_apex will still be compiled but it will be an empty package using conditional compilation.