tests: Implement Travis-based Multi-OS CI service

This commit implements (after the example of taskwarrior) a Travis-based
multi-OS continuous integration service, that tests on a variety of
Linux-based hosts and Mac OS X.

test/docker/ubuntu1804

@@ -0,0 +1,27 @@
+FROM ubuntu:18.04
+
+RUN apt-get update
+RUN apt-get install -y build-essential cmake git uuid-dev libgnutls28-dev libfaketime
+RUN apt-get install -y python
+
+# Setup language environment
+ENV LC_ALL en_US.UTF-8
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US.UTF-8
+
+# Setup timewarrior
+ADD . /root/code/
+WORKDIR /root/code/
+RUN git clean -dfx
+RUN git submodule init
+RUN git submodule update
+RUN cmake -DCMAKE_BUILD_TYPE=debug .
+RUN make -j2
+RUN make install
+RUN task --version
+
+# Setup tests
+WORKDIR /root/code/test/
+RUN make
+
+CMD ["bash", "-c", "./run_all -v ; cat all.log | grep 'not ok' ; ./problems"]