Move build steps for better caching strategy

Dockerfile

@@ -1,32 +1,13 @@
 FROM ultimaker/cura-build-environment:1
 
 # Environment vars for easy configuration
-ENV CURA_BENV_BUILD_TYPE=Release
-ENV CURA_BRANCH=docker
-ENV URANIUM_BRANCH=master
-ENV CURA_ENGINE_BRANCH=master
-ENV MATERIALS_BRANCH=master
 ENV CURA_APP_DIR=/srv/cura
 
 # Ensure our sources dir exists
 RUN mkdir $CURA_APP_DIR
 
-# Setup Uranium
-WORKDIR $CURA_APP_DIR
-RUN git clone -b $URANIUM_BRANCH --depth 1 https://github.com/Ultimaker/Uranium
-WORKDIR $CURA_APP_DIR/Uranium
-
-# Setup Cura
-WORKDIR $CURA_APP_DIR
-RUN git clone -b $CURA_BRANCH --depth 1 https://github.com/Ultimaker/Cura
-WORKDIR $CURA_APP_DIR/Cura
-
-# Setup materials
-WORKDIR $CURA_APP_DIR/Cura/resources
-RUN git clone -b $MATERIALS_BRANCH --depth 1 https://github.com/Ultimaker/fdm_materials materials
-WORKDIR $CURA_APP_DIR/Cura/resources/materials
-
 # Setup CuraEngine
+ENV CURA_ENGINE_BRANCH=master
 WORKDIR $CURA_APP_DIR
 RUN git clone -b $CURA_ENGINE_BRANCH --depth 1 https://github.com/Ultimaker/CuraEngine
 WORKDIR $CURA_APP_DIR/CuraEngine
@@ -38,6 +19,24 @@ RUN make install
 
 # TODO: setup libCharon
 
+# Setup Uranium
+ENV URANIUM_BRANCH=master
+WORKDIR $CURA_APP_DIR
+RUN git clone -b $URANIUM_BRANCH --depth 1 https://github.com/Ultimaker/Uranium
+WORKDIR $CURA_APP_DIR/Uranium
+
+# Setup materials
+ENV MATERIALS_BRANCH=master
+WORKDIR $CURA_APP_DIR/Cura/resources
+RUN git clone -b $MATERIALS_BRANCH --depth 1 https://github.com/Ultimaker/fdm_materials materials
+WORKDIR $CURA_APP_DIR/Cura/resources/materials
+
+# Setup Cura
+ENV CURA_BRANCH=docker
+WORKDIR $CURA_APP_DIR
+RUN git clone -b $CURA_BRANCH --depth 1 https://github.com/Ultimaker/Cura
+WORKDIR $CURA_APP_DIR/Cura
+
 # Make sure Cura can find CuraEngine
 RUN ln -s /usr/local/bin/CuraEngine $CURA_APP_DIR/Cura