Restrict toast width to screen size

[jzgom067]

Describe the bug
The max width of toasts is too wide for mobile displays.

To Reproduce
The best example of this is the "Name Autofilled" toast that displays on the painting page.

1. Log in
2. Set a nickname on the account
3. Go to the painting page on an event you haven't participated in yet
4. See the toast cut off on the screen

Expected behavior
Toasts should be constrained to the width of the screen, minus some padding.

Screenshots

Environment (please complete the following information):

• Platform: mobile
• OS: iOS
• Browser: Safari
• Version: v0.3.3