Fixes: #2248.
Add a close button to the seed backup warning banner in the wallet. The banner will reappear upon application restart as long as the seed hasn’t already been backed up (`profileModel.mnemonic.isBackedUp`).
A new .svg with a white outline needed to be added as well because the original “close.svg” had a purple outline, which would show up when the ColorOverlay applied to the close button had an opacity less than 1.0.
Eric Mastro