Check SMS is enabled before showing texting opts

[BryceStevenWilley]

• is_sms_enabled(), sees if the twilio config in the settings are non-empty (doesn't check that they work)
• Turns off mentions of texting in the "Share" page
• Turns off option to get texts from the reminder system
• Turns off options to text the link to yourself when signing

The only change I could see being suggested is to move is_sms_enabled() (and is_phone_or_email(), even thought it's been in AL for a while) to the Toolbox. IMO, it's not worth splitting highly coupled functions between two different packages, but will happily do it if suggested.

Fixes #411 for texting, not for email, but as mentioned in the meeting this morning, most of our users have some sort of email enabled on their server.

[BryceStevenWilley]

If we do make that change, we should use proper syntax - <br/> not <br>

I'm fine with changing it, but from what I understand, <br> is fine, <br/> is only necessary for XHTML