Fixed issue #9

Added play-slick plugin and reconfigured the database access layer for using the plugin.

1) Separate the Slick driver configuration to the application.conf file as db.default.slickdriver -- no need in view of play-slick plugin
2) Compact the database access such that all statements are executed in a single session -- play handles this internally through connection pools which are directly being used through the play-slick plugin
3) Create some way to ensure existence of tables and some basic data in the database and add option to create or delete them -- added method init() in DatabaseService for this functionality