Outermost WIP test to cover in-view behaviour and config
Implement a very simple feature flag

This allows people to switch a feature off or on with a config var.

This is different (and, I hope, complementary) to the mode approach.

My usecase is that UIKonf doesn't want to use the Motiviations feature,
so we want to switch it off, preferably without messing with any code.

Motivations may have several interactions with modes - Ruby Manor wants
to know your motivations before the event, but probably not in Archive
mode. The 'No motivations at all' need is orthogonal to the 'Motivations
then but not now' need.

I've deliberately kept this implementation as light as possible.
Extend Motivations feature flag coverage to the layout
Add routing feature flag helper

This allows us to only generate certain routes if a particular feature
is switched on...
Add feature flag to ApplicationController derived classes
Add instance-level feature method
Move Feature test so we can rename to FeatureFlag
Remove FeatureRouting because it's a duplicate

(Rename Feature to FeatureFlag)
rename Feature Flag feature to if_feature which seems better
Add block-based helpers for the common uses of can?

Almost all uses of `can?` in the views were for either `is-logged-in &&
can?(...)` or `is-not-logged-in && can?`. This provides helpers for
those cases. `user_can` (and `user_cannot`) along with `anyone_` and
`anonynmous_` versions of those.

This also adds an anonymous user object, `AnonymousUser`, which simply
claims to be anonymous, and the corresponding methods on `User`, which
claims not to be anonymous.

I'm not 100% sure of the names of the helpers, so I'm not opening a pull
request until I've slept on it. Thoughts welcome.
Rename `if_feature` and `anyone_cannot`

`if_feature` gets renamed back to `feature`

`anyone_cannot` becomes `no_one_can` because `anyone_cannot` is a stupid
name.
Remove the `feature` helper in favour of `anyone_can` et al

This simplifies things a bit and hopefully makes #38 happy...
Fix odd reverted features reference by, um, unreverting it.
Merge pull request #46 from fidothe/feature_flag_all_mode

mode-based feature flags