QA: Fixed "Upload image file" scenario

Fixed issue with early element center calculation during the CSS
transition in Chrome by waiting until navigation links are fully
visible. (The Chrome webdriver always clicks the center of an element
and may fail to calculate the right coordinates during animations.)

Change-Id: I2c22e872a8772090d0f508f6c7fa6df78b891a50
Setup A/B test for editing / performance

Does reloading page via JavaScript after edit encourage more editing?
Theoretically, re-rendering a page via JavaScript is quicker, but this
can vary depending on internet connection, size of page and various other
factors.

It is possible a slower editing experience might deter users from editing
further but we have no data to say one way or another.

This buckets our users into 2 groups
Bucket A: After editing the page will be reloaded via HTTP request
Bucket B: After editing the page will be re-rendered via JavaScript.

The purpose of the A/B test is to see if there are significantly more
edits under one bucket that another, or if there is no noticeable change
in behaviour.

Changes:
* Purposely remove the class from toast messages to ensure both test
conditions are the same.

Change-Id: I36208c0d6964685953a6bb2fc32eb7d15fe70834
Merge "QA: Fixed "Upload image file" scenario"
Merge "Setup A/B test for editing / performance"