Windup Distribution: Maven bom and submodule structure issues

There is some misconception in build system for Windup Distribution, Windup BOM and Windup Bootstrap modules.

1. https://github.com/windup/windup-distribution/blob/master/pom.xml#L39-L44 Windup BOM should be used only as IMPORT in DependencyManagement. There is no dependency to include as a pom file in Distribution

2. Windup BOM doesn't define Windup Bootstrap as managed dependency version

3. Windup parent and Windup Bootstrap defines duplicitly IMPORT of Windup BOM.