Added lastPlayed field on MediaFile.

core/src/main/sql/migrations/20151209054632-initial-schema-up.sql

@@ -23,6 +23,7 @@ CREATE TABLE media_files (
   file_hash VARCHAR NOT NULL,
   meta_info_source VARCHAR NOT NULL, -- 'tag' or 'filesystem'
   date_added TIMESTAMP NOT NULL DEFAULT NOW(),
+  last_played TIMESTAMP,
   comment VARCHAR DEFAULT ''
 );