Modified mail_remove_replies_after behaviour and added feature to strip gmail style replies

Created by: libregeek

The config item mail_remove_replies_after is modified to accept multiple marker strings. I have tested this with Outlook style(-----Original Message-----) and Zimbra style(----- Original Message -----) reply markers.

I'm not an expert in regular expressions, so I just kept both the implementations(gmail & outlook) different. May be we can store the regular expressions in mail_remove_replies_after and get rid of the hard coded gmail ( 7332a814 and ce630dd6 )

Added a regular expression to strip gmail style replies. This cannot be modified from the configuration page. The test results are included as a screenshot.