custom auth titles now use go through i18n

this is so when users switch between locales the custom titles also update
change API for custom auth titles
swap double for single quotes
Merge pull request #705 from moneyadviceservice/custom-titles-use-i18n

Custom titles use i18n
Add @enable-car_cost_tool to avoid test env requiring features.yml configuration
Merge pull request #706 from moneyadviceservice/enable_car_cost_tool_feature_flag_on_scenarios

Add @enable-car_cost_tool to avoid test env requiring features.yml config
bump budget_planner 4.0.0.641 => 4.0.0.642
bump budget_planner 4.0.0.642 => 4.0.0.643
Bump pensions_calculator from 0.2.0.467 to 0.2.0.478
Add mortgage_calculator gem from local dir. Add initializer for mortgage calculator
mount the engine.
add mortage calc assets to bower.json.erb
correctly handle the different urls for stamp duty and mortgage affordability tools.
Feature to test mortgage calculator integration.