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/).

view/src/main/AndroidManifest.xml

@@ -0,0 +1,3 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.termux.view">
+</manifest>