POC: Introduce Nextcloud based on Nginx web server.

UPDATE:
 - stack.yml contains FPM & Mariadb containers, updated names and hostnames for container
TODO:
 - update config.ini for trusted proxies support

This PR introduce POC of Nextcloud based on Nginx web server with php-fpm in separated container.
Basic installation with SQLite and few operations in web gui were tested.

Nginx dockerfile is generated from Dockerfile-nginx.template
  - FROM string has hardcoded variant - apache
  - There is no upstream PHP image with Nginx, due this generate-stackbrew-library is not able to identify parent correctly

New files were introduced in image:
  - Dockerfile-nginx.template
  - nginx-foreground
    + simulates behavior of apache2-foreground cmd
  - 16.0/nginx/Dockerfile
    + generated from template Dockerfile-nginx.template
  - nextcloud.confx
    + Nginx vhost configuration
  - start_net.sh (temporary)
    + Helper script to create user-defined network for Docker
    + '--link' option for docker create is obsolete and we need communication between fpm and nginx container
  - start_container.sh (temporary)
    + Helper script to handle containers
  - Dockerfile
    + /Dockerfile for verification purposes
Updated files:
  - set -x added to all shell scripts for easier troubleshooting (temporary)
  - update.sh
    + New variant introduced
    + Number of builded variant is limited for simplified CI.
  - .travis.yml (temporary)
    + Image push to registry for testing purposes
  - docker-entrypoint.sh
    + Recognizes new argument for entrypoint - nginx-foreground

Be careful during review, github recognizes removed files for 15.0 release as renamed to 16.0/nginx variant

Motivation/Usecase:
  - I have openvz based VPS where only old Docker 1.10 is supported.
  - Apache(in nextcloud container) in combination Nginx as a reverse proxy for multiple vhosts doesn't work correctly

Image pull link:
docker pull 1john2ci/nextcloud:apache-20190509
docker pull 1john2ci/nextcloud:fpm-20190509
Travis CI test: 530329740

Deployment notes:
  - Clone source code
  - Create user-defined network for Docker
  - Start fpm container
  - Start nginx container

Signed-off-by: Malanik Jan <malanik.jan@gmail.com>

start_mariadb.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# ##
+# file name: star_mariadb.sh
+# Author: Malanik Jan
+# Email: malanik (_dot_) jan (_at_) gmail (_dot_) com
+# Description: 
+#   - Helper script to start Mariadb
+# ##
+
+set -x
+
+MARIA_NAME='mariadb'
+MARIA_VOL='/srv/mariadb:/var/lib/mysql:rprivate' 
+MARIA_TAG='10.4.4-bionic'
+MARIA_IMAGE="${MARIA_NAME}:${MARIA_TAG}"
+
+docker stop "${MARIA_NAME}"
+docker rm "${MARIA_NAME}"
+
+eval "CMD='docker run -dit \
+    --hostname "${MARIA_NAME}" \
+    --name "${MARIA_NAME}" \
+    --net 'nextcloud' \
+    --volume ${MARIA_VOL} \
+    -e MYSQL_ROOT_PASSWORD='mariadb_admin' \
+    -e MYSQL_DATABASE='nextcloud' \
+    -e MYSQL_USER='ncd_admin' \
+    -e MYSQL_PASSWORD='ncd_admin' \
+    "${MARIA_IMAGE}"
+  '"
+${CMD}