Refactor keypair handling and expose storing keypairs on ffi

The user-visible change here is that it allows the FFI API to save
keys in the database for a context.  This is primarily intended for
testing purposes as it allows you to get a key without having to
generate it.

Internally the most important change is to start using the
SignedPublicKey and SignedPrivateKey types from rpgp instead of
wrapping them into a single Key object.  This allows APIs to be
specific about which they want instead of having to do runtime checks
like .is_public() or so.  This means some of the functionality of the
Key impl now needs to be a trait.

A thid API change is to introduce the KeyPair struct, which binds
together the email address, public and private key for a keypair.

All these changes result in a bunch of cleanups, though more more
should be done to completely replace the Key type with the
SignedPublicKye/SignedPrivateKey + traits.  But this change is large
enough already.

Testing-wise this adds two new keys which can be loaded from disk and
and avoids a few more key-generating tests.  The encrypt/decrypt tests
are moved from the stress tests into the pgp tests and split up.

python/src/deltachat/account.py

@@ -118,6 +118,18 @@ class Account(object):
         assert res != ffi.NULL, "config value not found for: {!r}".format(name)
         return from_dc_charpointer(res)
 
+    def _save_self_keypair(self, addr, public, secret):
+        """See _dc_save_self_keypair() in deltachat.h.
+
+        In other words, you don't need this.
+        """
+        res = lib._dc_save_self_keypair(self._dc_context,
+                                        as_dc_charpointer(addr),
+                                        as_dc_charpointer(public),
+                                        as_dc_charpointer(secret))
+        if res == 0:
+            raise Exception("Failed to set key")
+
     def configure(self, **kwargs):
         """ set config values and configure this account.
 

python/tests/test_account.py

@@ -1,4 +1,5 @@
 from __future__ import print_function
+import py
 import pytest
 import os
 import queue
@@ -9,6 +10,17 @@ from datetime import datetime, timedelta
 from conftest import wait_configuration_progress, wait_successful_IMAP_SMTP_connection, wait_securejoin_inviter_progress
 
 
+@pytest.fixture
+def datadir():
+    """The py.path.local object of the test-data/ directory."""
+    for path in reversed(py.path.local(__file__).parts()):
+        datadir = path.join('test-data')
+        if datadir.isdir():
+            return datadir
+    else:
+        pytest.skip('test-data directory not found')
+
+
 class TestOfflineAccountBasic:
     def test_wrong_db(self, tmpdir):
         p = tmpdir.join("hello.db")
@@ -24,6 +36,12 @@ class TestOfflineAccountBasic:
         ac1 = Account(p.strpath, os_name="solarpunk")
         ac1.get_info()
 
+    def test_save_self_keypair(self, acfactory, datadir):
+        ac = acfactory.get_unconfigured_account()
+        ac._save_self_keypair("alice@example.com",
+                              datadir.join('key/alice-public.asc').read(),
+                              datadir.join('key/alice-secret.asc').read())
+
     def test_getinfo(self, acfactory):
         ac1 = acfactory.get_unconfigured_account()
         d = ac1.get_info()