Regions for country list

Country list segmentation to be able to assign countries to specific regions. Tasks:

• DONE adding new table:

CREATE TABLE `civicrm_worldregion` (
`id` INT( 10 ) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`name` VARCHAR(256) NOT NULL
) ENGINE=MyISAM ;

• DONE adding new column to civicrm_country table: region_id
• populating civicrm_region and civicrm_country with proper region<->country assignments
• providing UI for displaying the region in contact's location block
• providing the way to search for contacts/activities/cases in specific region
• we'll not implement UI for editing regions list at this stage (potential changes will be done directly in the database)