Simple cleanup.

* Locked Teaspoon version in Gemfile to 0.7.9; 0.8 requires changes I don't want/need to deal with now;
* Updated other Gem versions in Gemfile.lock;
* Disabled Growl notifications for UniformNotifier in config/environments/development.rb; not every machine we build this on *has* Growl;
* Fixed old copy-and-paste bug in config/initializers/session_store.rb.

RSpec: 4 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 9 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2
Inadvertent omission from earlier commit: updated config/application.rb

This silences the now-infamous deprecation warning "I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message." We force it to true, which is the new preferred setting (and contrary to the old, implied default setting).

RSpec: 4 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 9 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2