Returns only present keys in Token Response

Thanks to @AzizLight for feedback on
https://github.com/applicake/doorkeeper/issues/220

Ref: http://tools.ietf.org/html/rfc6749#page-35

[fixes #220]
Allow to overwrite scope in routes + specs
Use attr_accessible if ProtectedAttributes gem is present
Merge pull request #204 from adriandulic/master

Allow to overwrite scope in routes
Merge pull request #290 from jsmestad/bugfix/check-for-strong-parameters-in-rails-4

Use attr_accessible if ProtectedAttributes gem is present
Update CHANGELOG to reflect what is currently "unreleased"
Merge pull request #291 from jsmestad/patch-1

Update CHANGELOG to reflect what is currently "unreleased"
CHANGELOG update
Merge remote-tracking branch 'applicake/master' into fix_token_expiration
Udated test to provide expires_in_seconds on the mocked access_token, wrote comment explaining test behavior for 'expires_in'
Releasing v0.7.3
Merge pull request #228 from centro/fix_token_expiration

Fix token response `expires_in` value to be relative to request time
Updates CHANGELOG [ci skip]

Note: Version 1.0.0 is not what was being prepared by @felipeelias, as
he couldn't continue maintaining doorkeeper. I bump the mayor version
cause I introduce a backwards incompatible change, following Semantic
Versioning: http://semver.org/.
Content adjustment. [fixes #109]
added ActionController::Instrumentation in TokensController
Updated CHANGELOG
Merge pull request #293 from soul-rebel/tokens_controller_instrumentation

added ActionController::Instrumentation in TokensController
Fix mock and stub deprecation warnings.
Fix mock and stub deprecation warnings.
Changed generation behavior on Application save

The callbacks that generate client uid and  secret for the Application
model will now check if one is already provided. If so, it will not
generate a new uid or secret.

In Rails 4, mass assignment security is done in the controller. Added
extra specs to ensure MAS.