new icon fetching service. remove besticon dep.

src/Icons/Dockerfile

@@ -2,17 +2,9 @@ FROM microsoft/aspnetcore:2.0.6
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-        unzip \
         gosu \
     && rm -rf /var/lib/apt/lists/*
 
-WORKDIR /tmp
-COPY iconserver.sha256 .
-RUN curl -L -o iconserver.zip https://github.com/mat/besticon/releases/download/v3.6.0/iconserver_linux_amd64.zip \
-    && sha256sum -c iconserver.sha256 \
-    && unzip iconserver.zip -d /etc/iconserver \
-    && rm iconserver.*
-
 ENV ASPNETCORE_URLS http://+:5000
 WORKDIR /app
 EXPOSE 5000