Breadcrumbs implementation
refactor, code improvement.
API: test invalid get param name.
API tests: minor code improvements.
API: test Topmost Concepts with Factories.
API: some code improvement.
API: test related concepts with factories.
API: test all concept relatives with factories.
API: test get concept with factories.
API: test has concept with factories.
API: test all translations for concept with factories.
API: test available languages with factories.
API: test available thesauri with factories.
API: test fetch themes with factories.
API: test fetch groups with factories.
fix status code for 404 view.
Tests: adapt tests to the new 404 status code.
urls: remove namespace from urls, run django in subpath.
docs: add property value length explanation, searchText description.
layout: replace hard-coded url.