Add the native Hesychia Android client so the repo can build beyond the placeholder README.

.gitignore

@@ -2,9 +2,11 @@
 # Gradle files
 .gradle/
 build/
+**/build/
 
 # Local configuration file (sdk path, etc)
 local.properties
+keystore.properties
 
 # Log/OS Files
 *.log
@@ -14,6 +16,7 @@ captures/
 .externalNativeBuild/
 .cxx/
 *.apk
+*.aab
 output.json
 
 # IntelliJ
@@ -33,3 +36,5 @@ google-services.json
 # Android Profiling
 *.hprof
 
+# OS
+.DS_Store