Move PerformanceTestUtils from core to usage/test-support
Adds load tests

- testing number of concurrent apps that can be started, and number
  of apps that can be managed.
don't let stringify convert `null` to `"null"`
compute UPTIME sensor
fix bug where nginx up-detection continued to run after service stoppage
remove the hand from sensor/config values, as they aren't clickable
use generics for RendererHint, simplify class hierarchy there, and add support for rendering based on class type, used for Duration and HostAndPort, and for Entity instances to show the name of the entity
Add type coercion for parameterized collections and their entries
Fix some formatting for clarity
Use coerce method with TypeToken when setting configuration
Add new parser for object DTOs in YAML DSL
Make coerced collections immutable
Deprecate extra JcloudsLocationCustomizer keys and add test for management context injection
Remove deprecation and type coercion adapter from ProxySslConfig
Force deep resolution of Map and Iterable ConfigKeys
Changed to commons-beanutils to construct objects and added more tests
Fix serialisation and persistence issues
Change coerced collection type and make mutable again
Add support for Configurable object creation using ConfigKeys and flags
This closes #182

* github/pr/182:
  Add support for Configurable object creation using ConfigKeys and flags
  Change coerced collection type and make mutable again
  Fix serialisation and persistence issues
  Changed to commons-beanutils to construct objects and added more tests
  Force deep resolution of Map and Iterable ConfigKeys
  Remove deprecation and type coercion adapter from ProxySslConfig
  Deprecate extra JcloudsLocationCustomizer keys and add test for management context injection
  Make coerced collections immutable
  Add new parser for object DTOs in YAML DSL
  Use coerce method with TypeToken when setting configuration
  Fix some formatting for clarity
  Add type coercion for parameterized collections and their entries