[CI] Add CI Docker stuff

Once you have login in docker, just run `cd .ci-docker/ && make` to
build and publish the CI docker image

.ci-docker/Dockerfile

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+FROM openjdk:8-jdk
+RUN apt-get -y update
+RUN DEBIAN_FRONTEND=noninteractive apt-get install -y apt-utils
+RUN DEBIAN_FRONTEND=noninteractive apt-get dist-upgrade -y
+RUN DEBIAN_FRONTEND=noninteractive apt-get install -y wget tar unzip lib32stdc++6 lib32z1 git
+
+ENV ANDROID_COMPILE_SDK "28"
+ENV ANDROID_BUILD_TOOLS "28.0.3"
+ENV ANDROID_SDK_TOOLS "4333796"
+
+WORKDIR /opt/
+RUN wget --quiet --output-document=android-sdk.zip https://dl.google.com/android/repository/sdk-tools-linux-${ANDROID_SDK_TOOLS}.zip
+RUN unzip -q -d android-sdk-linux android-sdk.zip
+RUN echo y | android-sdk-linux/tools/bin/sdkmanager "platforms;android-${ANDROID_COMPILE_SDK}" >/dev/null
+RUN echo y | android-sdk-linux/tools/bin/sdkmanager "platform-tools" >/dev/null
+RUN echo y | android-sdk-linux/tools/bin/sdkmanager "build-tools;${ANDROID_BUILD_TOOLS}" >/dev/null
+RUN yes | android-sdk-linux/tools/bin/sdkmanager --licenses
+
+WORKDIR /tmp/
+RUN git clone --depth=1 https://gitlab.com/tom79/mastalab
+WORKDIR /tmp/mastalab
+RUN chmod +x gradlew
+RUN ANDROID_HOME=/opt/android-sdk-linux PATH=$PATH:/opt/android-sdk-linux/platform-tools/ ./gradlew tasks
+RUN ANDROID_HOME=/opt/android-sdk-linux PATH=$PATH:/opt/android-sdk-linux/platform-tools/ ./gradlew assembleDebug
+RUN ANDROID_HOME=/opt/android-sdk-linux PATH=$PATH:/opt/android-sdk-linux/platform-tools/ ./gradlew --stacktrace -Pci --console=plain :app:testFdroidDebugUnitTest
+RUN ANDROID_HOME=/opt/android-sdk-linux PATH=$PATH:/opt/android-sdk-linux/platform-tools/ ./gradlew --stacktrace -Pci --console=plain :app:lintFdroidDebug -PbuildDir=lint

.ci-docker/Makefile

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+all:
+	docker build -t tom79/mastalab-ci:latest . && docker push tom79/mastalab-ci:latest