webadmin: refactor—overgrown constructor

- overgrown constructor split to smaller, single purpose methods
(I need to add next gui code there, and it's too long already)
- make all parameters final, if they can be final, not just some.

Change-Id: I05d1ec1064eb3ec4ce17f88a2d532cb76aa4f39d
Signed-off-by: Martin Mucha <mmucha@redhat.com>