Add duration and type to talks

While making this change I learned that alembic doesn't create Enum
types in Postgres when altering an existing table. The approach used
here was taken from a Stack Overflow linked to from Google Groups.

References #1
Stub talk submission page

This is a work in progress.

References #1
Initial talk submission

While some work still needs to be done, this is an initial working
version of the talk submission page. In addition to this page, the user
dashboard page is being added. The dashboard allows a user to access the
talks they've submitted and edit them.

Closes #1
Add site header

This is the site's header. The logo needs to be updated with the new
dates, but everything else should be in order, at least to get started.
Fix routing
Remove registration URL

This should be put back once registration is live.
Adjust padding

The padding is being removed below the header on the home page. Padding
is being added around items in drop down menus.
Use correct Flask-Mail settings

`DEFAULT_MAIL_SENDER` was the setting in a very old version of the
library.