Initial fix for Bug 408042

Automatically create a new working set based on
root project name on maven project import.
Addressed comments in Bug 408042

1. place new checkbox below existing working set creation area
so as to make the two buttons look connected
2. Update label on new button with working set name when a new 
root project is selected.

See:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=408042#c7