This is a squash commit for @cydh's pull request #1299.
Cleaned up the `char_del_option` checks.
Added a comment for `char_del_option`, that only work for clients that send delete request by using 0x0068 or 0x01fb.
Added an enum for values.
Added a function to validate and adjust configuration data.
Resolved character deletion not working properly for clients 2015-10-01 and higher (fixes#1189)
Delete date should be sent as remaining time on some client versions.
Adjusted some comment wording.
Added empty/default birthdate deletion.
Made email deletion case insensitive.