[cfid-598] Made Yaml servlet initializer more generic (no UAA refs)

The servlet initializer had some hardcoded references UAA_* environment
variable names.  This change removes those and makes them configurable
via the servlet context.

[#44222845] [cfid-598] remove small uaa.yml from war file
[cfid-598] Add NestedMapPropertySource and use it to create Environment
[cfid-598] Heavy refactoring of Yaml reading