Output build files should have an optional external destination

[josephnobes-stfc]

When using a parent application specific repository that relies on LOKI to build, it can be confusing to have to drill down into the structure of LOKI to find the output files (especially when this directory will also contain many other build outputs that are not actually required by the used).

Therefore it should be optional to specify a different output directory where the relevant output files will be copied to.