No longer use volume for Matomo install

Having the code base in a volume makes upgrades and migrations a pain,
additionaly the file copies on initial startup can be really slow on NFS
drives.

Having a volume allows for the dynamic installation of plugins, but then
that is specific to that instance, if you were to run a several stage
environment dev/stage/prod then one would need to manually check that
the plugins exist is each environment. Better would be to extend the
image and pack the plugins in with the installation.

@see matomo-org/docker#57
@see matomo-org/docker#161

matomo/Dockerfile

@@ -36,7 +36,7 @@ ENV \
     MATOMO_USER_NAME=admin \
     MATOMO_USER_PASS='$2y$10$S38e7HPM9LI3aOIvcnRsfuMCm4ipNP572QsvbCK60upoHVJ61hMrS'
 
-COPY --from=download --chown=nginx:nginx /opt/matomo /opt/matomo
+COPY --from=download --chown=nginx:nginx /opt/matomo /var/www/matomo
 
 COPY rootfs /