Introduce "retrieve_package" functional to manage package downloading #24

Job	Run time
Build with Intel toolchain	7m 19s
Build extra components with GNU toolchain	22m 30s
Build without LCAO and MPI	4m 12s
Build without LCAO	5m 37s
Build without MPI	6m 48s
Build with CUDA support	15m 26s
Build with GNU toolchain	8m 48s
Build extra components with Intel toolchain	18m 52s
Build without ELPA	8m 40s
	1h 38m 12s

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