adds api calls for getting, setting, removing

- using Ecto queries, the api can now get newest
  message or get the last message
- delete all messages of a sender id
- add a message (auto adding a time stamp)

lib/bump/messages/message.ex

@@ -5,8 +5,7 @@ defmodule Bump.Messages.Message do
   schema "messages" do
     field :sender, :string
     field :data, :string, default: ""
-    field :timestamp, :utc_datetime, default: DateTime.utc_now |> DateTime.truncate(:second)
-
+    field :timestamp, :utc_datetime
     timestamps()
   end