not emit old changes in feed mod
bug fix; performance improve; new color theme

* improve scrapy performance by periodically dispatch
* use feedparser on bytes to avoid encoding issue
* add footer links option
* use tomorrow color theme
* hide mod selector before inited
* fix bug in sending notice to multiple emails of one user
* add jinja2 md5 filter to support md5 based full page update notice
* not emit old changes in feed mod, to deal with bad feed