Fix emoji insertion in MySQL

Switch to utf8mb4 instead of utf8 because f*** MySQL
See https://github.com/doctrine/dbal/pull/851

app/config/parameters.yml.dist

@@ -19,16 +19,18 @@ parameters:
     database_path: "%kernel.root_dir%/../data/db/wallabag.sqlite"
     database_table_prefix: wallabag_
     database_socket: null
+    # with MySQL, use "utf8mb4" if got problem with content with emojis
+    database_charset: utf8
 
-    mailer_transport:  smtp
-    mailer_host:       127.0.0.1
-    mailer_user:       ~
-    mailer_password:   ~
+    mailer_transport: smtp
+    mailer_host: 127.0.0.1
+    mailer_user: ~
+    mailer_password: ~
 
-    locale:            en
+    locale: en
 
     # A secret key that's used to generate certain security-related tokens
-    secret:            ovmpmAWXRCabNlMgzlzFXDYmCFfzGv
+    secret: ovmpmAWXRCabNlMgzlzFXDYmCFfzGv
 
     # two factor stuff
     twofactor_auth: true