Improve mail types feature

Improve the "mail types" feature, that allow for categorization of loaded emails:

• add specific XObject for a "Matcher" (a pattern defining how a mail matches a particular type)
• allow to use regular expression, or simple string contains for a matcher (advanced mode)
• allow to switch "ignore case" and "multi-line" without having to know how to set flags in regular expression
• allow to apply specific operator between matchers (AND/OR only for now, and the same applies on all matchers)
• improve UI to manage that new XObject (at creation, only one matcher can be defined)