Add storage library (and demo app)

and use for periodic files backup
diff --git a/.gitignore b/.gitignore
index ec60569..0146d1a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,7 +6,7 @@
 
 ## Intellij
 out/
-lib/
+/lib/
 .idea/*
 !.idea/runConfigurations*
 !.idea/inspectionProfiles*
@@ -33,7 +33,8 @@
 
 ## NetBeans
 **/nbproject/private/
-build/
+/build/
+/app/build/
 nbbuild/
 dist/
 nbdist/
@@ -50,6 +51,3 @@
 
 ## Android
 gen/
-
-## Prebuilt
-Backup.apk