[META] Create a node by sending an email

Problem/Motivation

Support node creation from an incoming email. A new Inmail analyzer plugin for nodes should analyze the content of an incoming email message and create a node in case identified user (sender) has enough permissions to do it. A node created via email will be logged. Extend proof-of-concept plugin built in first weeks. Introduce an Inmail MailFooter plugin that should process the body of an email. Footer plugin should support limited number of footer variations. The basic cases that are going to be supported are including a regex match for "-- \n" (RFC3676) cutoff line and "On ... wrote" part which is de-facto standard within Gmail. MailFooter plugin will separate the email into real mail body and footer parts. From there, we can remove unnecessary signature/footer and the rest with a body field of a node. Subject of an email will be used as a node title. Subject must be provided in: “[node][node_type] Node title” format in order to map the node type we creating a node for.