Split up into modules and add float module

Split the app/ module into three modules

terminal/ - Terminal emulator library module.
view/ - Terminal view library module (depending on terminal/).
app/ - The main Termux app (depending on view/).

Also add the

float/ - The Termux:Float app (depending on view/).

float/src/main/res/layout/activity_permission.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              android:orientation="vertical"
+              android:layout_width="match_parent"
+              android:gravity="center"
+              android:layout_height="match_parent">
+
+    <TextView
+        android:layout_gravity="center"
+        android:text="@string/draw_overlay_permission_explanation"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"/>
+
+    <LinearLayout
+        android:layout_gravity="center_horizontal"
+        android:gravity="center_horizontal"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content">
+    <Button
+        android:layout_marginTop="24dp"
+        android:text="@string/grant_permission"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:onClick="onOkButton"/>
+    </LinearLayout>
+
+</LinearLayout>