GitLab

- scons 2.5.1 requires 2.7
- updated email

- corrected version in editable environments

fixed wrong boost include dir

require install tool for SystemLibsInstallBuilder

implemented better version support for 3rdparty libraries

- explicitly added include targets

- fixes bug that we cannot easily change lib versions
- less prone to errors when different versions of libs have different
  dependencies
- consolidated structure of build files

- corrected default list of libdirs to search

- how can we chose between library versions

Feature 9 verify   package behavior when target is already built

See merge request !16

- this ensures always up to date values in substituted files