samples: mesh: nrf52: Transition Time support, Coding Style

Added transition time support. Now if NODE received optional
parameters then they would get entertained by it.

Added two new models that is Generic Default Transition Time
Server & Client resp. to complete overall architecture to
support newly introduced architecture.

With this it was possible to implement
gen_move_set/gen_move_set_unack message handlers.

Removed redundancy from App & revised overall implementation.
Fixed Bugs. Upgraded coding style. Added & replaced comments to
improve code readability. Improved printk messages.

Signed-off-by: Vikrant More <vikrant8051@gmail.com>