Richify (#653)

* Improved rich_echo, added rich_echo_via_pager

* Initial implementation for #647, added rich output

tests/plugins/env_vars.py

@@ -0,0 +1,8 @@
+import os
+
+import pytest
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_load_initial_conftests(args, early_config, parser):
+    os.environ["OSXPHOTOS_IS_TESTING"] = "1"