Bug 513559 - Provide OAuth client parameter encapsulation

- abstract OAuthParameters object to be implemented by clients with
  concrete values
- constructors based on parameter object
- support overriding credentials based on client "name" for testing purposes
- add support to USS Browser view to use OAuthParameters

Bug: 513559
Change-Id: I8ca63ca89ffef4b6a675605222b0f937b2c088ff
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=513559
Signed-off-by: Carsten Reckord <reckord@yatta.de>
Signed-off-by: Brian de Alwis <bsd@mt.ca>