Make elementToAppend take priority over domID for sandbox configs

[codetheweb]

Closes #2885.

[orta]

Looks good to me

[jakebailey]

Seems fine to me, though I'm assuming this is a part of a published package, in which case I'm holding off those kinds of PRs a little until I can... figure out how exactly to bump and publish these packages correctly.

[orta]

Merges to v2 run pleb - which compares the versions in the package.json for any non-private package in the packages folder and then npm publishes them if that version is not present - there's a small writeup here: #130 (comment)

[jakebailey]

With bump versions with #2904 to minimize the waiting within the current infrastructure.