refactor the loading of a conference out into a single place
prevent a list of sessions being loaded when it is not valid to see them

We do still want to link to individual sessions, but not show the whole
list
prevent a list of speakers being loaded when it is not valid to see them

We do still want to link to individual speakers, but not show the whole list
switch to the built in method for 404s
null check
prevent unauthorised editing of items
Prevent users from editing other users' profiles + tests
add some tests to check that the complete list of speakers and sessions cannot be seen when not appropriate
add more tests to confirm that actions cannot be performed on sessions of other users
Add argument checking
Rename the attribute
Extract the constructor of the controller into a helper method
Remove redunadant check
Merge branch 'lock-down-pages' of git://github.com/adrianbanks/dddeastanglia into adrianbanks-lock-down-pages

Conflicts:
	DDDEastAnglia/Controllers/SessionController.cs
	DDDEastAnglia/Controllers/SpeakerController.cs
	DDDEastAnglia/Views/Shared/_Layout.cshtml