Don't copy over package versions into package-list for bootstrap.

* This decouples the versions referenced by the architecture-specific
  repository file from the actual versions available in the haikuports
  branch that happens to be used for the bootstrap build.
Make set of source packages for bootstrap-image configurable.

* Add new build profile 'minimum', which defines a minimum set of
  packages.
* Introduce HAIKU_BOOTSTRAP_SOURCES_PROFILE and let it default to
  '@minimum-raw'. This can be overruled in UserBuildConfig, setting
  it to '@release-raw' will cause all source packages required for a
  full release to be put onto the bootstrap-image.
* Add new image HaikuImageMinimum, which is meant to define the minimum
  useful Haiku image (yeah, I know that's vague).
* Add HAIKU_MINIMUM_BUILD, which indicates that HaikuImageMinimum should
  be used (it would be better to merge this with HAIKU_BOOTSTRAP_BUILD
  into something like HAIKU_BUILD_TYPE)
* Cleanup duplicate references to basic packages - those are now added
  by the topmost Jamfile (no longer referenced by the build profiles).