Add play to backup bookstack, reorganize files

ansible/roles/core.yml

@@ -0,0 +1,5 @@
+---
+- hosts: core
+  become: yes
+  roles:
+  - core

ansible/roles/docker.yml

@@ -0,0 +1,5 @@
+---
+- hosts: docker-host
+  become: yes
+  roles:
+    - docker