added travis testing

travis builds and spins up containers for sqlite, mariadb and postgres
and runs a simple python test script for accessing the wallabag.

tests/docker-compose.postgresql.yml

@@ -0,0 +1,24 @@
+version: '2'
+services:
+  wallabag:
+    build:
+      context: ../
+    image: wallabag:postgresql
+    container_name: wallabag
+    environment:
+      - POSTGRES_PASSWORD=my-secret-pw
+      - POSTGRES_USER=my-super-user
+      - SYMFONY__ENV__SECRET=F00B4R
+      - SYMFONY__ENV__DATABASE_DRIVER=pdo_pgsql
+      - SYMFONY__ENV__DATABASE_HOST=db
+      - SYMFONY__ENV__DATABASE_PORT=5432
+      - SYMFONY__ENV__DATABASE_NAME=wallabag
+      - SYMFONY__ENV__DATABASE_USER=wallabag
+      - SYMFONY__ENV__DATABASE_PASSWORD=wallapass
+    ports:
+      - "127.0.0.1:80:80"
+  db:
+    image: postgres
+    environment:
+      - POSTGRES_PASSWORD=my-secret-pw
+      - POSTGRES_USER=my-super-user