Fix potential ReferenceError in non-browser env

Testing for `window` would throw if undeclared.
Also, avoid repeating feature check.
Enable Rails-specific rubocop tests and fix warnings.
Fix typo / strange presence of `double`.
Merge pull request #761 from moneyadviceservice/enable_rails_specific_rubocop_checks

Enable Rails-specific rubocop tests and fix warnings.
Opt users in to the newsletter by default
Don't need to manually forward argument to super
Merge pull request #759 from moneyadviceservice/4233_opt_users_in_by_default

Opt users in to the newsletter by default
Merge pull request #758 from stevoland/master

Fix potential ReferenceError in non-browser env
Fix missing trailing comma in JSHint config.
Merge pull request #762 from moneyadviceservice/fix_jshint_config

Fix missing trailing comma in JSHint config.
Replace Kramdown gem with Mastalk
update pensions_calculator version. Update syndication layout.
Merge pull request #764 from moneyadviceservice/update_pensions_calculator

update pensions_calculator version. Update syndication layout.
Add links to the landing page
Change EN content
Add CY content to the landing_page
Add youtube video to the landing page
tools/annuties routes to landing pages controller
Add annuities template
Add breadcrumbs to annuities pages