Saner page-per-thing urls

Here's what this PR sets our URLs to:

    /performance/carers-allowance/realtime
    /performance/carers-allowance/claims
    /performance/carers-allowance/digital-takeup
    /performance/carers-allowance/completion-rate
    /performance/carers-allowance/journey
    /performance/carers-allowance/availability
    
    for FCO in [deposit-foreign-marriage, pay-foreign-marriage-certificates, pay-legalisation-drop-off, pay-legalisation-post, pay-register-birth-abroad, pay-register-death-abroad]:
    
    /performance/FCO/realtime
    /performance/FCO/applications
    /performance/FCO/completion-rate
    /performance/FCO/journey
    /performance/FCO/availability
    
    /performance/housing/starts-and-completions
    /performance/housing/regional-transactions
    /performance/housing/first-mortgage
    /performance/housing/house-price-index

    /performance/g-cloud/company-size
    /performance/g-cloud/proportion-sme
    /performance/g-cloud/customers
    /performance/g-cloud/spend-by-lot
    
    /performance/gov-uk/realtime
    /performance/gov-uk/device-type

Feedback is obviously appreciated.