Updated Dockerfile to support JPEG files in docker. Fixes issue #115.

Dockerfile

@@ -1,16 +1,24 @@
 FROM php:7-apache
 
-RUN apt-get update &&  apt-get install -y curl libcurl4-openssl-dev libicu-dev libpng-dev gnupg zip libzip-dev libonig-dev libxslt-dev && rm -rf /var/lib/apt/lists/*
+# Install needed dependencies for PHP build
+RUN apt-get update &&  apt-get install -y pkg-config curl libcurl4-openssl-dev libicu-dev \
+    libpng-dev libjpeg-dev libfreetype6-dev gnupg zip libzip-dev libonig-dev libxslt-dev vim \
+    && apt-get -y autoremove && apt-get clean autoclean && rm -rf /var/lib/apt/lists/*
 
+# Install GD (we have to configure GD first before installing it, see issue #115)
+RUN docker-php-ext-configure gd --with-freetype --with-jpeg && docker-php-ext-install gd
+# Install other needed PHP extensions
 RUN docker-php-ext-install pdo_mysql curl intl mbstring bcmath gd zip xml xsl
 
 # Install yarn
 RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
 RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
-RUN apt-get update && apt-get install -y yarn
+RUN apt-get update && apt-get install -y yarn && apt-get -y autoremove && apt-get clean autoclean && rm -rf /var/lib/apt/lists/*
 
+# Install composer
 COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
 
+# Set working dir
 WORKDIR /var/www/html
 COPY --chown=www-data:www-data . .
 
@@ -20,6 +28,7 @@ COPY ./.docker/symfony.conf /etc/apache2/sites-available/symfony.conf
 RUN a2ensite symfony.conf
 RUN a2enmod rewrite
 
+# Install composer and yarn dependencies for Part-DB
 USER www-data
 RUN composer install -a --no-dev && composer clear-cache
 RUN yarn install && yarn build && yarn cache clean