Rename CMB2_hookup to CMB2_Hookup #1328

viktor@mail:~/cmb2$ grep -rFn CMB2_hookup
includes/CMB2.php:232:          add_action( "cmb2_init_hookup_{$this->cmb_id}", array( 'CMB2_hookup', 'maybe_init_and_hookup' ) );
includes/CMB2_hookup.php:14:class CMB2_hookup extends CMB2_Hookup_Base {
includes/CMB2_Options_Hookup.php:14:class CMB2_Options_Hookup extends CMB2_hookup {
includes/CMB2_Options_Hookup.php:119:                   add_action( "admin_print_styles-{$page_hook}", array( 'CMB2_hookup', 'enqueue_cmb_css' ) );
includes/helper-functions.php:331:              CMB2_hookup::enqueue_cmb_css();
includes/helper-functions.php:335:              CMB2_hookup::enqueue_cmb_js();
bootstrap.php:53:        * Get all created metaboxes, and instantiate CMB2_hookup