Feature Improvement: Throttle multiple consecutive Likes

Currently, if you were to toggle the Like button found in Jetpack's sharing buttons, a 'Like' notification is sent to the site owner's email and mobile device (if applicable) for each individual Like. This can be a vector for spam/harrassment.

#### Steps to reproduce the issue

1. Go to any test site with Sharing enabled.
2. Click on Like
3. Click on Like again to deselect it
4. Repeat steps 2 and 3 as many times as you need

#### What I expected
I expected that consecutive Likes on the same post by the same user would result in some form of lock out message, such as is seen with comments

#### What happened instead
In my tests, I am able to repeatedly spam the Like button and send as many notifications as I like to the site owner.

**Screenshots**
Screenshot of email notifications

#### Potential Fix
Perhaps some sort of lock out after consecutive Likes


Start at Jetpack's Sharing Like button and follow the existing email and mobile notification flow for repeated toggles. The issue names no files or tests; define the lockout behavior and verify that consecutive Like and unlike actions no longer produce unbounded notifications.

Written by the indexing model from the issue text.