EPi:VisitedPages cookie uses wrong limiter

Description

Currently, EPi:VisitedPages cookie uses a semicolon ';' as a delimiter if several of the visited pages' criteria are used in the same visitor group. However, according to the specification (see https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2), multiple header values should be separated by a comma ','.

Steps to reproduce
1. Create a visitor group with two different VisitedPages criteria (for different pages).
2. Visit both pages that are part of the criteria.
3. Look at the EPi:VisitedPages cookie.

Expected result:
Pages should be part of the cookie value.

Actual:
Only one of the pages is part of the cookie value.