scroll bars for the ParseTreeView

src/ui/android/res/layout/alternative_item.xml

@@ -21,7 +21,7 @@
     
 	<org.grammaticalframework.ui.android.ParseTreeView
     	android:id="@+id/desc_details"
-    	android:layout_width="wrap_content"
+    	android:layout_width="match_parent"
     	android:layout_height="wrap_content"
     	android:layout_below="@id/alternative_desc"
         android:textSize="25sp"

src/ui/android/res/values/attrs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+     <declare-styleable name="Theme">
+        <attr name="parseTreeViewStyle" format="reference"/>
+    </declare-styleable>
+</resources>

src/ui/android/res/values/styles.xml

@@ -15,6 +15,10 @@
     <!-- Application theme. -->
     <style name="AppTheme" parent="AppBaseTheme">
         <!-- All customizations that are NOT specific to a particular API-level can go here. -->
+        <item name="parseTreeViewStyle">@style/ParseTreeViewStyle</item>
+    </style>
+    
+    <style name="ParseTreeViewStyle">
+        <item name="android:scrollbars">horizontal</item>
     </style>
-
 </resources>