Git ignore file to add in the root of the project and in all of the modules.

.gitignore

###Android###

# built application files
*.apk
*.ap_

# files for the dex VM
*.dex

# Java class files
*.class

# generated files
bin/
gen/
out/
#generated tests
androidTest/

# gradle
.gradle/

# Local configuration file (sdk path, etc)
local.properties

# Gradle properties (users, etc)
gradle.properties

# Eclipse project files
.classpath
.project

# Proguard folder generated by Eclipse
proguard/

# Intellij project files (Android Studio)
*.iml
*.ipr
*.iws
.idea/
/build

# Windows
.DS_Store
Thumbs.db

#Mirror
mirror/

#Merge temp files
*.orig
*.bak