Build improvements: clang-tidy, sonar, Dockerfile. (#488)

Dockerfile

@@ -1,10 +1,36 @@
-FROM debian:latest
-RUN apt-get update && apt-get install -y cmake git g++ libimlib2-dev liblua5.3-dev libxext-dev libxft-dev libxdamage-dev libxinerama-dev ncurses-dev
-COPY . /root/
-RUN mkdir /root/build
-WORKDIR /root/build
+FROM ubuntu:latest
+RUN apt-get update \
+  && apt-get install -y \
+       cmake \
+       git \
+       g++ \
+       libimlib2-dev \
+       liblua5.3-dev \
+       libxext-dev \
+       libxft-dev \
+       libxdamage-dev \
+       libxinerama-dev \
+       ncurses-dev
+
+COPY . /conky
+WORKDIR /conky/build
 ARG X11=yes
-RUN sh -c 'if [ "$X11" = "yes" ] ; then cmake ../ ; else cmake -DBUILD_X11=OFF ../ ; fi'
-RUN make all
-RUN make install
+
+RUN sh -c 'if [ "$X11" = "yes" ] ; then cmake ../ ; else cmake -DBUILD_X11=OFF ../ ; fi' \
+  && make -j5 all \
+  && make -j5 install \
+  && apt-get remove -y \
+       cmake \
+       git \
+       g++ \
+       libimlib2-dev \
+       liblua5.3-dev \
+       libxext-dev \
+       libxft-dev \
+       libxdamage-dev \
+       libxinerama-dev \
+       ncurses-dev \
+  && rm -rf /var/lib/apt/lists/* \
+  && rm -rf /conky \
+
 CMD conky