Added support for user certs (#714)

To support connecting to Kodi over SSL using self-signed certificates
we need to allow this explicitly for Android versions 6 and higher.

app/src/main/AndroidManifest.xml

@@ -17,7 +17,8 @@
     <application
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
-        android:label="@string/app_name">
+        android:label="@string/app_name"
+        android:networkSecurityConfig="@xml/network_security_config">
 
         <!-- Activities -->
         <activity

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

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