Emails and Messages improvements

Hi Tuan,

1. As you implemented Common Tags recently, why would not to add default COMPANY_SIGNATURE tag for new installations? Thus, instead of changing "Regards, Company Name" in almost 60 messages we can change only one Tag.

2. There are some needless inline styles on span and strong tags in some messages. Please switch your editor to CodeMirror and navigate to the Legacy Emails and Messages, you should see some inconsistency. Also there are empty paragraphs at the end of some messages.

Thanks!