Update .gitignore files for Android Studio

Without these, Git shows lots of noisy build/IDE config files.

These files are based on these two sources (plus the list of added files that Git shows when I build in Android Studio):
https://github.com/github/gitignore/blob/master/Android.gitignore
https://github.com/github/gitignore/pull/2103/files

tensorflow/contrib/lite/java/demo/.gitignore

@@ -1,9 +1,29 @@
+# This file is based on https://github.com/github/gitignore/blob/master/Android.gitignore
 *.iml
+.idea/compiler.xml
+.idea/copyright
+.idea/dictionaries
+.idea/gradle.xml
+.idea/libraries
+.idea/inspectionProfiles
+.idea/misc.xml
+.idea/modules.xml
+.idea/runConfigurations.xml
+.idea/tasks.xml
+.idea/workspace.xml
 .gradle
-/local.properties
-/.idea/workspace.xml
-/.idea/libraries
+local.properties
 .DS_Store
-/build
+build/
+gradleBuild/
+*.apk
+*.ap_
+*.dex
+*.class
+bin/
+gen/
+out/
+*.log
+.navigation/
 /captures
 .externalNativeBuild

tensorflow/examples/android/.gitignore

@@ -0,0 +1,29 @@
+# This file is based on https://github.com/github/gitignore/blob/master/Android.gitignore
+*.iml
+.idea/compiler.xml
+.idea/copyright
+.idea/dictionaries
+.idea/gradle.xml
+.idea/libraries
+.idea/inspectionProfiles
+.idea/misc.xml
+.idea/modules.xml
+.idea/runConfigurations.xml
+.idea/tasks.xml
+.idea/workspace.xml
+.gradle
+local.properties
+.DS_Store
+build/
+gradleBuild/
+*.apk
+*.ap_
+*.dex
+*.class
+bin/
+gen/
+out/
+*.log
+.navigation/
+/captures
+.externalNativeBuild