Login/register activities

[PinewoodPip]

Activities need to be created for the log in and register process.

This is fairly low priority since any account-related functionality won't be added until much later, but at the same time the views are easy to implement to make the prototype look more fleshed out.

• [x] The FormCard fragment with TextField should be reused for the text fields for a consistent appearance
• [x] "Register" button in login activity should transition to the register activity
• [x] Make the sign in and skip buttons transition to the main activity as a placeholder
• [x] We might want to reuse the checkbox + label combo; create a fragment for it

[PinewoodPip]

"Forgot password" would be nice to have, though I'm not sure how to achieve it - I think it requires some firebase setup to be able to send emails.

Additionally, the ability to enter as a guest needs to be removed. It will not be supported in the end.