Revert "Replace old html by css"

See http://kb.mailchimp.com/article/how-to-code-html-emails

This reverts commit 7ff33715c5cdd122efbc6b67937bb1bd615d39c3.
Months in lowercase

Signed-off-by: Emilien Kenler <hello@emilienkenler.com>
Remove css and restore old html code to keep compatibility with webmails

Signed-off-by: Emilien Kenler <hello@emilienkenler.com>