feat(ci): weekly backup

Closes #12

See merge request core-services/r3lab/r3-pages!11

.gitlab-ci.yml

 # In case something goes horribly wrong, you can fall back to `image: ruby:latest`
 image: git-r3lab.uni.lu:4567/r3/docker/jekyll-lcsb:1.0
 
+stages:
+  - build
+  - deploy
+  - backup
+
 build the website:
   stage: build
   before_script:
@@ -34,3 +39,20 @@ Deploy to production:
     - ssh -p $SSHPORT $SSHCONNECT "mkdir -p ~/web/r3lab_$CI_JOB_ID"
     - scp -P $SSHPORT -r build/* $SSHCONNECT:~/web/r3lab_$CI_JOB_ID
     - ssh -p $SSHPORT $SSHCONNECT "cd ~/web/latest && ln -fs ../r3lab_$CI_JOB_ID/* . && cd .. && find . -type d -name 'r3lab*' -not -newermt '-1 minutes' -exec rm -rf {} +"
+
+
+## Backups
+Create the backup:
+  stage: backup
+  image: alpine:3.1
+  when: manual
+  before_script:
+    - 'which ssh-agent || ( apk add --update openssh )'
+    - eval $(ssh-agent -s)
+    - echo "$SSHPRIVKEY" | tr -d '\r' | ssh-add - > /dev/null
+    - mkdir -p ~/.ssh && chmod 700 ~/.ssh
+    - 'echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'
+    - echo "$KNOWNHOSTS" > ~/.ssh/known_hosts
+    - chmod 644 ~/.ssh/known_hosts
+  script:
+    - ssh -p $SSHPORT $SSHCONNECT "mkdir -p ~/web/latest ~/backups/; cd ~/web/; tar -zchvf ~/backups/backup_$(date +'%Y_%m_%d').tar.gz latest"