Haketilo

fix URL construction when downloading definitions from Hydrilla

make "uuid" an optional property

automatically pick up a free port to run the HTTP proxy on

It is now possible to run multiple make test commands in parallel (e.g. testing abrowser and librewolf simultaneously after running configure for each of them in 2 different directories).

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