Disable button on form submission with progress indication

[petusa]

• Font Awesome progress indicator/spinner Icon added to Get Beta Access
  button in a declarative way
• dependencies added to Gemfile and assets application resources
  (js/css)
• en/de language files updated with please_wait translation
• Gemfile.lock updated
• previous obsolete code parts removed => I know it has just been
  replaced lately

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[petusa]

I signed it! Thanks, Peter / petusa

…

On Thu, May 25, 2017 at 3:19 PM, googlebot ***@***.***> wrote: Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA). 📝 *Please visit https://cla.developers.google.com/ <https://cla.developers.google.com/> to sign.* Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks. ------------------------------ - If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data <https://cla.developers.google.com/clas> and verify that your email is set on your git commits <https://help.github.com/articles/setting-your-email-in-git/>. - If you signed the CLA as a corporation, please let us know the company's name. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#163 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AJfQvYyUW_CzNkrdHJpuz1aSmIUQ825Vks5r9WPVgaJpZM4NmQ-L> .

[googlebot]

CLAs look good, thanks!