Removing old before_filter.

This was supposed to be removed with @dbd88e, but I completely forgot
it.
Redirect correctly after registration.

'Correctly' is purely defined by being in accordance with the tests and
passing them.
Cleaning up code.

Changes are largely inspired by the Ruby Style Guide [1] and includes
the following.

* Removing unnecessary return statements
* Removing parentheses around conditionals
* Removing control flow statements with negative conditions

The following example show a bad control flow.

  if not anything
    do_something
  else
    do_something_else
  end

I would rewrite it like this.

  if anything
    do_something_else
  else
    do_something
  end

* Utilizing Rails' #try [2]

This enables us to remove statements like

  current_user and corrent_user.admin

and replace them with the simple statement

  current_user.try(:admin)

* Replacing `or` and `and` with `||` and `&&`, respectively, where
  appropriate

`or` and `and` are control flow operators and does not behave the same
way as their seemingly similar alternatives [3].

* Removing ternary operators returning only boolean values

  current_user.includes_dinner = params[:dinner] == "yes" ? true : false

..is the same as

  current_user.includes_dinner = params[:dinner] == "yes"

* Fixing spelling errors

Examples include 'uncomplete', 'adress'.

* Removing unnecessary references to `self`
* Removing unnecessary .gitkeep files

[1] https://github.com/bbatsov/ruby-style-guide
[2] http://api.rubyonrails.org/classes/Object.html#method-i-try
[3] http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/
Removing unnecessary helpers for associations.

These can automatically be generated by #belongs_to by giving it right
options. See the documentation [1] for all possible configurations.

[1]
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html
Cleaning up relation between Order and User.

An 'owned_order' association has been added to User, which works on the
owner_user_id column of Order. The creation of a default order has been
moved from the controller action orders#show into the User model, where
it belongs. This is cleaner and it simplifies the controller code.
Made TalkTypesController require admin.
Utilizing inheritance to create an admin factory.

Read more about it in the documentation [1].

[1]
https://github.com/thoughtbot/factory_girl/blob/master/GETTING_STARTED.md#inheritance
Test of AddDefaultScheme is done without Sponsor.

The use of Sponsor within the tests of AddDefaultScheme obviously
changed the behavior of Sponsor and with a certain run-order of tests,
it caused race conditions. This changes the tests by creating a dummy
class and extending that.
Fixing volatile test.

This is the same fix to SponsorsController tests as @2eafb6 was to
TalkTypesController and TalkCategoriesController.
Testing required authentication for actions.

Three macro methods have been implemented:

 * should_not_require_authentication
 * should_require_user_authentication
 * should_require_admin_authentication

These tests actions with authentication ensured by #authenticate_user!
or #require_admin. The following controller actions does not have
trivial authorization logic and cannot be tested using these macros.

 * payments#new_paypal
 * payments#new_manual
 * payments#create_manual
 * talks#edit
 * talks#destroy
Merged conflic
Forgot to add this in @46eb09d.
Not allowing ticket_type of Ticket to be nil.

I see no reason for why which this should be allowed.
Changing redirect behavior after registration.

Users of each ticket type will now be redirected to different pages.
Users of free tickets ends up on the front page, users of talk tickets
ends up on the page for creating a talk and users of regular tickets
ends up on the order page.
Fixing a typo in a User test.
Changing the auto-create-order behavior of User.

The model now behaves in a way that an order is automatically created if
a user associated with a regular ticket is saved. If it is not
associated with such a ticket, the order associated with the user from
beforehand is destroyed.