change Space::FindNearestTo to use a new GetNearest in NearBodyFinder
add Space::GetBodiesNear which is like GetBodiesMaybeNear but filters more
remove the Space::BodyNearIterator and use 'auto' instead
extend Space::GetBodiesMaybeNear to filter its result set by object type
code style
exclude the origin body from Space::GetBodiesMaybeNear(Body*) results
exclude dead bodies from the Space::GetBodiesMaybeNear result list
make missiles and ECM work over frame boundaries
simplify missile trigger detection