Make foldable settings in EncryptActivity a separate widget

OpenPGP-Keychain/src/main/res/values/attr.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <declare-styleable name="FoldableLinearLayout">
+        <attr name="foldedLabel" format="string" />
+        <attr name="unFoldedLabel" format="string" />
+        <attr name="foldedIcon" format="string" />
+        <attr name="unFoldedIcon" format="string" />
+    </declare-styleable>
+
+</resources>