feat: display a Toast when reCAPTCHA fails while users are filling up a form

[jia1]

Problem

Closes #31

Solution

Display a Toast when the captcha module's on-error handler is fired.

Features:

1. The Toast does not show up immediately upon page load. It takes a bit of time (5 seconds) to show up after a user first touches the form (e.g. clicking on a form field). User does not need to fill up anything. He/she just needs to touch the form.
2. The Toast shows up at the same time as the reCAPTCHA failure at the bottom of the form (this is good).

Before & After Screenshots

BEFORE:
Only the reCAPTCHA failure at the bottom of the form will be observed after the user touches the form.

AFTER:
Both Toast at the top and reCAPTCHA failure at the bottom will be observed.

[karrui]

The error on your screenshot does not seem to be the error in your commit?

[jia1]

@karrui my bad. I took that screenshot before updating the message to the correct one. I went to take the new screenshot and updated it here. Thanks for the catch!

[karrui]

@syan-syan is the copywriting good enough? Should we also prompt the user to refresh or? Or tell the user that submission will fail?

[karrui]

lgtm! approve first, can always update wording later

[r00dgirl]

@karrui @jia1 sorry for some reason these notifs sometimes get filtered to junk. the copy is fine. thanks!