Fix Travis CI and add build cache

Also remove relicts from Android.mk file

.travis.yml

@@ -3,6 +3,28 @@ android:
   components:
   - build-tools-28.0.3
   - android-28
+
+licenses:
+  - android-sdk-license-.+
+  - '.+'
+
+before_install:
+  - mkdir "$ANDROID_HOME/licenses" || true
+  - echo -e "\n8933bad161af4178b1185d1a37fbf41ea5269c55" >> "$ANDROID_HOME/licenses/android-sdk-license"
+  - echo -e "\nd56f5187479451eabf01fb78af6dfcb131a6481e" >> "$ANDROID_HOME/licenses/android-sdk-license"
+  - echo -e "\n24333f8a63b6825ea9c5514f83c2829b004d1fee" >> "$ANDROID_HOME/licenses/android-sdk-license"
+  - echo -e "\n84831b9409646a918e30573bab4c9c91346d8abd" >> "$ANDROID_HOME/licenses/android-sdk-preview-license"
+
+before_cache:
+  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
+
+cache:
+  directories:
+    - $HOME/.gradle/caches/
+    - $HOME/.gradle/wrapper/
+    - $HOME/.android/build-cache
+
 deploy:
   provider: releases
   api_key:

app/src/main/Android.mk

@@ -32,7 +32,4 @@ LOCAL_CERTIFICATE := platform
 LOCAL_STATIC_JAVA_LIBRARIES := commons-io
 LOCAL_SRC_FILES := $(call all-java-files-under, java)
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
-LOCAL_STATIC_ANDROID_LIBRARIES := \
-	androidx.preference_preference \
-	androidx.lifecycle_lifecycle-extensions
 include $(BUILD_PACKAGE)