Titles and authors on posts

Added `title` field to `posts` table and changed type of `posttime`
field for easier manipulation in PHP. Display author and title on posts.
Changed register button to register link and added missing table column
on header form to fix HTML5 validation. Fixed PHP errors showing when
attempting to log in with an unregistered email address. Prevent users
from registering with the nickname "Anonymous" so that posts without an
author cannot be confused for posts by a user with that name. Explicitly
assign style properties to several elements in notes in preparation for
compose system that will have a different set of element types that
share the same styles as the existing ones.
Implemented post compose

Show a compose sticky note that is styled after other notes with the
exception of color palette. index.php now will commit a note when
newtitle and newnote POST variables are present, and will either print
out only the newly created note (for AJAX) or the entire updated page
(for reloading the page after a POST) depending on whether the client
has JavaScript enabled or not. If the client has JavaScript enabled, the
compose note and its contents will autosize when modified and
subsequently rearrange surroundings notes when focus is lost so that
there are absolutely no scrollbars; otherwise, compose note stays a
constant size and will have scrollbars in its message body area if
enough lines are typed.