Haketilo

fix test-environment* targets

fix out-of-source builds

improve the build system

assume and use "$schema" properties in item definitions

facilitate running test environment with Haketilo loaded into browser

fix loading initial data and verify it in automated tests

change store names and data keys to singular

prevent failure in setup of the test case being run after test_broadcast ( old IceCat)

make resource dependency specifier an object

adapt to changes in file path format

From now on we assume Hydrilla serves file contents at 'file/sha256/' instead of 'file/sha256-'.
With this commit we also stop using the "hash_key" property internally.