Bug Fix: #4359 Notices on create table page.

Bug Fix: #4359 Notices on create table page.

1)

    Notice in ./libraries/tbl_columns_definition_form.inc.php#147
    Undefined variable: available_mime

    Backtrace

    ./tbl_create.php#92: require(./libraries/tbl_columns_definition_form.inc.php)

2)

    Notice in ./libraries/tbl_columns_definition_form.inc.php#149
    Undefined variable: mime_map

    Backtrace

    ./tbl_create.php#92: require(./libraries/tbl_columns_definition_form.inc.php)

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>