Add a detailed pricing page

[Kun Xi]

The pricing page should cover all of our SKUs:

• one child
• sibling
• punch card: 5x, 10x
• group discount: 6x, 15x
• birthday parties

[Kun Xi]

Also need to update the nginx rewrite rule to redirect /pricing.html to /pricing/

[Kun Xi]

fix #19: add the pricing page for all SKUs.

→ <<cset 095efbe780e3>>