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_lowlevel.py

@@ -1,5 +1,5 @@
 from __future__ import print_function
-from deltachat import capi, const, set_context_callback, clear_context_callback
+from deltachat import capi, cutil, const, set_context_callback, clear_context_callback
 from deltachat.capi import ffi
 from deltachat.capi import lib
 from deltachat.account import EventLogger
@@ -83,3 +83,18 @@ def test_markseen_invalid_message_ids(acfactory):
     msg_ids = [9]
     lib.dc_markseen_msgs(ac1._dc_context, msg_ids, len(msg_ids))
     ac1._evlogger.ensure_event_not_queued("DC_EVENT_WARNING|DC_EVENT_ERROR")
+
+
+def test_provider_info():
+    provider = lib.dc_provider_new_from_email(cutil.as_dc_charpointer("ex@example.com"))
+    assert cutil.from_dc_charpointer(
+        lib.dc_provider_get_overview_page(provider)
+    ) == "https://providers.delta.chat/example.com"
+    assert cutil.from_dc_charpointer(lib.dc_provider_get_name(provider)) == "Example"
+    assert cutil.from_dc_charpointer(lib.dc_provider_get_markdown(provider)) == "\n..."
+    assert cutil.from_dc_charpointer(lib.dc_provider_get_status_date(provider)) == "2018-09"
+    assert lib.dc_provider_get_status(provider) == const.DC_PROVIDER_STATUS_PREPARATION
+
+
+def test_provider_info_none():
+    assert lib.dc_provider_new_from_email(cutil.as_dc_charpointer("email@unexistent.no")) == ffi.NULL