Add provider info functions to the FFI API

A lot of work from @Hocuri and @Simon-Laux mostly.

This exposes the API of the deltachat-provider-overview crate on the
deltachat FFI API, allowing clients to use it to help users set up
their accounts.

python/tests/test_provider_info.py

@@ -0,0 +1,27 @@
+import pytest
+
+from deltachat import const
+from deltachat import provider
+
+
+def test_provider_info_from_email():
+    example = provider.Provider.from_email("email@example.com")
+    assert example.overview_page == "https://providers.delta.chat/example.com"
+    assert example.name == "Example"
+    assert example.markdown == "\n..."
+    assert example.status_date == "2018-09"
+    assert example.status == const.DC_PROVIDER_STATUS_PREPARATION
+
+
+def test_provider_info_from_domain():
+    example = provider.Provider("example.com")
+    assert example.overview_page == "https://providers.delta.chat/example.com"
+    assert example.name == "Example"
+    assert example.markdown == "\n..."
+    assert example.status_date == "2018-09"
+    assert example.status == const.DC_PROVIDER_STATUS_PREPARATION
+
+
+def test_provider_info_none():
+    with pytest.raises(provider.ProviderNotFoundError):
+        provider.Provider.from_email("email@unexistent.no")