Show all transports on the dashboard

and indicate which transports are currently available.
The icons have been chosen from the official material icons and might be
replaced later with icons that better represent the given transport.

Please note that I used vector drawables which will be automatically
converted at build time to raster graphics.

Closes #96

briar-android/res/layout/list_item_transport.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:orientation="horizontal"
+	android:layout_width="match_parent"
+	android:layout_height="wrap_content"
+	android:padding="@dimen/margin_small"
+	android:gravity="center_horizontal">
+
+	<ImageView
+		android:id="@+id/imageView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:padding="@dimen/margin_small"
+		tools:src="@drawable/transport_tor"/>
+
+	<TextView
+		android:id="@+id/textView"
+		android:layout_width="wrap_content"
+		android:layout_height="match_parent"
+		android:gravity="center_vertical"
+		android:padding="@dimen/margin_small"
+		android:textColor="@android:color/tertiary_text_light"
+		tools:text="@string/transport_tor"/>
+
+</LinearLayout>

briar-android/res/layout/transports_list.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	android:orientation="vertical"
+	android:layout_width="wrap_content"
+	android:layout_height="wrap_content">
+
+	<View
+		android:layout_width="match_parent"
+		android:layout_height="1px"
+		android:background="@color/horizontal_border"/>
+
+	<GridView
+		android:id="@+id/transportsView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:padding="@dimen/margin_medium"
+		android:numColumns="3"/>
+
+</LinearLayout>