Add assignment form jumps on page reload

While testing MDL-39929, Dave spotted that assignment form page jumps, when page gets loaded.

Steps to reproduce:

1. Click to add new assignment
2. On assignment form anchor is about a third of the way down the page when the page loads.

Please find attached screenshots in linked issue.

1. Integration_master_add_assignment_form.png - this shows the page scrolled down upon page load (no interaction from the user). This is taken from the integration master branch
2. Integration_27_add_assignment_form.png - this shows the same page once loaded (no interaction from the user). Note that the page hasn't been anchored and is fully scrolled up. This is more desirable behaviour. This is taken from the integration 2.7 branch.

This was observed using chrome on Ubuntu. When using Firefox on Ubuntu, instead of the page being anchored a third of the page down, the page is only anchored roughly 20 pixels down.