Adds a new network_security_config to allow custom CAs installed by user. This is needed for Android 7+, see https://android-developers.googleblog.com/2016/07/changes-to-trusted-certificate.html.

app/src/main/res/xml/network_security_config.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<network-security-config>
+    <base-config cleartextTrafficPermitted="true">
+        <trust-anchors>
+            <certificates src="system" />
+            <certificates src="user" />
+        </trust-anchors>
+    </base-config>
+</network-security-config>