Merge branch 'ubuntu-baseimage' into 'master'

pull ubuntu:18.04 insted of python:2.7 from Docker repo.

See merge request !1

Dockerfile

-FROM python:2.7
+# +--------------------------------------+
+# | You need to get calibre-web first!   |
+# | Just do a 'git clone ...' and put    |
+# | Calibre-Web into './calibre-web', so |
+# | the build-command can copy it into   |
+# | the Docker-image.                    |
+# +--------------------------------------+
+
+FROM ubuntu:18.04
+
+RUN apt-get update
+RUN apt-get install -y python python-pip python-virtualenv
+RUN apt-get install -y imagemagick libmagickwand-dev
 
 # create a non-root user
 RUN groupadd -g 999 appuser && \
@@ -7,10 +19,8 @@ RUN groupadd -g 999 appuser && \
 RUN mkdir -p /app /ebooks
 WORKDIR /app
 
-# get GIT, then clone current master of calibre-web
-RUN apt-get update 
-RUN apt-get -y install git
-RUN git clone https://github.com/janeczku/calibre-web.git /app
+# copy calibre-web to /app
+COPY calibre-web/ /app/
 
 # install the requirements
 RUN pip install -r requirements.txt
@@ -19,10 +29,7 @@ RUN pip install -r requirements.txt
 RUN pip install -r optional-requirements.txt
 
 # install lxml
-RUN pip install lxml
-
-# install imagemagick from debian
-RUN apt-get install -y imagemagick libmagickwand-dev
+# RUN pip install lxml
 
 # install policy.xml into /etc/ImageMagick
 COPY policy.xml /etc/ImageMagick-6/policy.xml