SMTP configuration through environment

Configuring SMTP parameters required to be written in files which is not
convenient when using docker containers as the credentials need to be in
the filesystem.

Created environment parameters override for those parameters. A new build
script created in order to generate those parameters right before
launching the application.

composer.json

@@ -85,6 +85,9 @@
             "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
             "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
             "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
+        ],
+        "build-parameters": [
+            "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters"
         ]
     },
     "extra": {
@@ -92,7 +95,13 @@
         "symfony-web-dir": "web",
         "symfony-assets-install": "relative",
         "incenteev-parameters": {
-            "file": "app/config/parameters.yml"
+            "file": "app/config/parameters.yml",
+            "env-map": {
+                "mailer_host": "WALLABAG_MAILER_HOST",
+                "mailer_user": "WALLABAG_MAILER_USER",
+                "mailer_password": "WALLABAG_MAILER_PASSWORD",
+                "secret": "WALLABAG_SECRET"
+            }
         }
     },
     "autoload": {