add docker compilation to travis (#3433)

* add docker compilation to travis

add new matrix entry in .travis.yml for compiling on 18.04
add Dockerfile in .ci to build ubuntu 18.04 inside docker
remove release entry for uvuntu 16.04 to not conflict
refactor .travis.yml
refactor travis-comile.sh
merge travis-dependencies.sh into the travis.yml
remove travis-dependencies.sh

* enable debugging on travis-compile.sh

* set ubuntu16 buildtype to "Debug"

set buildtype Debug for as requirement for "test"
add --debug and --release flags to travis-compile.sh

* make output prettier

edit the format warning message and clangify.sh output

* fix clangify.sh

fix --cf-version flag
fix directory argument parsing
add directory parsing details to --help
add examples to --help

.ci/Dockerfile

@@ -0,0 +1,20 @@
+FROM ubuntu:bionic
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        bc \
+        build-essential \
+        clang-format \
+        g++ \
+        git \
+        cmake \
+        libprotobuf-dev \
+        libqt5multimedia5-plugins \
+        libqt5svg5-dev \
+        libqt5sql5-mysql \
+        libqt5websockets5-dev \
+        protobuf-compiler \
+        qt5-default \
+        qttools5-dev \
+        qttools5-dev-tools \
+        qtmultimedia5-dev \
+    && rm -rf /var/lib/apt/lists/*