Add nightly build steps

* TODO: Do not run nightly builds, if no changes in `master` branch.

.drone.yml

@@ -4,13 +4,38 @@ type: docker
 name: default
 
 steps:
-- name: Build Dockerfile
+
+- name: Build & Publish Development Image
+  image: plugins/docker
+  settings:
+    repo: fbrinker/tileboard
+    dockerfile: Dockerfile.nightly
+    target: dev
+    tags: dev
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+
+- name: Build & Publish Nightly Image
+  image: plugins/docker
+  settings:
+    repo: fbrinker/tileboard
+    dockerfile: Dockerfile.nightly
+    target: nightly
+    tags: nightly
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+
+- name: Prepare Release Dockerfile
   image: alpine
   commands:
     - apk update && apk add bash curl grep jq sed
     - ./build.sh
 
-- name: Build & Publish Image
+- name: Build & Publish Release Image
   image: plugins/docker
   settings:
     repo: fbrinker/tileboard