Refactor POM to inherit from oparent. Remove local settings related to nexus and checkstyle.

The goals of oparent are to centrally define shared parent POM definitions such as nexus (distributionManagement) location, coding styles, license checks, coding style checks, sonar setup, etc.

Please review the change to see if this works for appc, and whether any changes need to be incorporated into oparent POMs. Thanks.