438559 Recommend extraRequirements instead of surefire-plugin deps.

- The dependencies parameter on the tycho-surefire-plugin has severe
  drawbacks: It does not work for intra-reactor dependencies, unless
  there is already a (Maven or Tycho-injected) dependency to the project
  building the dependency. Also, the <dependency> elements have a
  <version> although that value is interpreted as version range (causing
  parts of the confusion in bug 436617). Therefore, we now recommend
  to use extraRequirements in the target-platform-configuration instead.
- Also: Normalize indentation in documentation to three spaces, which
  turned out to be a good compromise on web pages.
- Also: Point to new dependency resolution wiki page in case of an
  dependency resolution error.
- Also: Fix exception message "cannot resolve target definition" because
  the "definition" and not the "file" is being resolved.

Bug: 438559
Bug: 436617
Change-Id: Ided945571c07f808d2ab823004b51578fbef6bdc