- remove dependence on /sim/number-views: the view manager just uses all

- remove dependence on /sim/number-views: the view manager just uses all
  /sim/view[*] that it finds. It's not only unnecessary that view definitions
  have subsequent indices, but aircraft are now *requested* to use indices
  100++. /sim/view[0] .. /sim/view[99] are reserved for the system. (Not
  that we'd ever need that many, This is just a convention, it's nowhere
  hard-coded.)
- replace the string operations for property paths by method calls & other
  improvements