Ensure that certain PostNode forms are validated

This means that the email and pgp fields are verified by regex, and the
contact and details field are required to be length 255 or under.
Require that messages be under 1000 characters

This is sort of a low limit, but also lowers the potential for abuse of
the instance's SMTP server.

Close #148
Update API docs somewhat
Added max-lengths to fields on message forms.
Added max-lengths on creating node form
Added message "basic markdown is supported"
Merge branch 'f.safer-forms'

Conflicts:
	res/web/js/form.js
Fixed issue with message showing the message button
Removed alert()
Started to improve menu for sending messages.

Ref #124 - [x] Provide reload button for captcha
Allow re-try on captcah if it's wrong.

Closes #124