Changed capability for admin menu page from 'level 8' (deprecated) to 'manage_options'

Info:
http://codex.wordpress.org/Roles_and_Capabilities#User_Levels
Added js and css files loading to properly WordPress hooks

Info:
http://codex.wordpress.org/Function_Reference/wp_enqueue_script#Notes
Fixed multiple PHP E~Notices on plugin settings save
Deleted php close tags in end of php files

Info:
http://php.net/manual/en/language.basic-syntax.instruction-separation.php
Merge pull request #1 from versusbassz/master

Some PHP E~Notices fixed and some corrections for compliance to Wordpress coding standards