adds senders to database and firebase connect

- senders, which now have a firebase token
  are added as their own table in the database
- firebase token api call added, which allows
  a user to connect a sender id to a firebase token
- firebase library not yet connected to the saved
  firebase tokens

lib/bump/database.ex

@@ -1,6 +1,7 @@
 defmodule Bump.Database do
   alias Bump.Repo
   alias Bump.Messages.Message
+  alias Bump.Senders.Sender
   import Ecto.Query
 
   def pop(sender) do
@@ -58,5 +59,8 @@ defmodule Bump.Database do
 
   end
 
+  def addSender(sender, %{"firebase" => firebase}) do
+    Repo.insert(%Sender{sender: sender, firebase_token: firebase})
+  end
 
 end