docker: add dockerfiles for Ubuntu 18.04 (Bionic)

docker/DockerfileBionic

+FROM docker.pkg.github.com/savoirfairelinux/opendht/opendht-deps-bionic:2.0.0
+MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+
+RUN git clone https://github.com/savoirfairelinux/opendht.git \
+	&& cd opendht && mkdir build && cd build \
+	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr \
+		-DOPENDHT_PROXY_CLIENT=On \
+		-DOPENDHT_PROXY_SERVER=On \
+		-DOPENDHT_C=On \
+		-DOPENDHT_PYTHON=On \
+		-DOPENDHT_LTO=On \
+		&& make -j8 && make install \
+	&& cd ../.. && rm -rf opendht

docker/DockerfileDepsBionic

+FROM ubuntu:18.04
+MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+
+RUN echo "APT::Acquire::Retries \"3\";" > /etc/apt/apt.conf.d/80-retries
+RUN apt-get update && apt-get install -y \
+        apt-transport-https build-essential cmake git wget libncurses5-dev libreadline-dev nettle-dev \
+        libgnutls28-dev libuv1-dev cython3 python3-dev python3-setuptools libcppunit-dev libjsoncpp-dev \
+        autotools-dev autoconf libasio-dev libfmt-dev libhttp-parser-dev libmsgpack-dev \
+    && apt-get clean
+
+# libasio-dev (1.10) is too old
+RUN echo "** Building a recent version of asio ***" \
+    && wget https://github.com/chriskohlhoff/asio/archive/asio-1-12-2.tar.gz \
+    && tar -xvf asio-1-12-2.tar.gz && cd asio-asio-1-12-2/asio \
+    && ./autogen.sh && ./configure --prefix=/usr --without-boost \
+    && make install \
+    && cd ../../ && rm -rf asio*
+
+RUN echo "*** Downloading RESTinio ***" \
+    && mkdir restinio && cd restinio \
+    && wget https://github.com/aberaud/restinio/archive/8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59.tar.gz \
+    && ls -l && tar -xzf 8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59.tar.gz \
+    && cd restinio-8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59/dev \
+    && cmake -DCMAKE_INSTALL_PREFIX=/usr -DRESTINIO_TEST=OFF -DRESTINIO_SAMPLE=OFF \
+             -DRESTINIO_INSTALL_SAMPLES=OFF -DRESTINIO_BENCH=OFF -DRESTINIO_INSTALL_BENCHES=OFF \
+             -DRESTINIO_FIND_DEPS=ON -DRESTINIO_ALLOW_SOBJECTIZER=Off -DRESTINIO_USE_BOOST_ASIO=none . \
+    && make -j8 && make install \
+    && cd ../../ && rm -rf restinio*