Add Fundraising Banner with next TBB security update

Let's plan to add a fundraising banner with the next TBB security update (TBB 8.5.3) which should happen around 2019-07-09.

The banner should come off on the following TBB security update, which should happen around 2019-09-03.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information