Adding index.php with silence is golden security method

See
https://github.com/tommcfarlin/WordPress-Plugin-Boilerplate/commit/bef3a5f669f93b651979b30beff05ec9015b0c75
Removed translation/pot/text domain code & files

Will do translations in a later release.
Added custom 772x250 PNG banner image

Removed high-DPI 1544x500 placeholder PNG banner image.
Reference: http://wordpress.org/plugins/about/faq/