Install imagemagick by conda rather than apt

Hopefully, this will help R's magick package compile better against it.

Dockerfile

@@ -8,7 +8,7 @@ USER root
 # Also install ocaml and dependency rlwrap for L2 CS course by Kim Nguyen
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-        openssh-client rsync unison less tree curl gdb imagemagick libmagick++-dev libopenjp2-7 \
+        openssh-client rsync unison less tree curl gdb libopenjp2-7 \
         ocaml rlwrap dune js-of-ocaml libjs-of-ocaml \
         net-tools traceroute iputils-ping \
         time \

environment.yml

@@ -27,6 +27,7 @@ dependencies:
 # Some additional packages that don't have a specific repo yet
 
 # Visualisation
+- imagemagick    # used e.g. by R package animation, and many more
 - matplotlib
 - cycler         # missing matplotlib dependency: https://stackoverflow.com/questions/44419333/matplotlib-cant-find-cycler