feat: Implement recaptcha verification

[atm1504]

Fixes #2348 , #2319

Changes:

Screenshots for the change:
Will be updated once complete

[atm1504]

@iamareebjamal should we have this feature. This was implemented as discussed in the Gitter channel, regarding the changes in the server-side script.
But, @liveHarshit shared some comments fossasia/open-event-attendee-android#1943 (comment) where it was discussed that ReCaptcha won't be needed in the android clients. Can you please confirm what should I do?

[iamareebjamal]

Discuss this with SUSI server guys

[atm1504]

Discuss this with SUSI server guys

We had a discussion regarding this in the gitter channel, they said to implement recaptcha.

[atm1504]

@iamareebjamal please review it. Also, please tell where to store the API key.

[ci-reporter]

The build is failing

✨ Good work on this PR so far! ✨ Unfortunately, the Circle CI build is failing as of 3ff7a72. Here's the output:

lint check

> Task :app:preBuild UP-TO-DATE

I'm sure you can fix it! If you need help, don't hesitate to ask a maintainer of the project!

---

Failed build for de75047

lint check

> Task :app:preBuild UP-TO-DATE

Failed build for 21ed178

lint check

> Task :app:preBuild UP-TO-DATE

---

This comment was automagically generated by ci-reporter. If you see a problem, open an issue here.

[ci-reporter]

The build is failing

✨ Good work on this PR so far! ✨ Unfortunately, the Circle CI build is failing as of 21ed178. Here's the output:

lint check

> Task :app:preBuild UP-TO-DATE

I'm sure you can fix it! If you need help, don't hesitate to ask a maintainer of the project!

---

This comment was automagically generated by ci-reporter. If you see a problem, open an issue here.

[mariobehling]

Please fix Travis.

[mariobehling]

Please provide a screenshot.

[mariobehling]

Same comment as in the other PR: We cannot keep the API key in the app itself. This would be a security issue. It should be added during building of the app using Travis environment variables. Please implement it in that way.

[batbrain7]

@atm1504 please refer to the way youtube API key is stored in the App.

[batbrain7]

This PR is open for a long time, if anyone wants to take this up, they can