Only create a Ymacs sandbox if Ymacs is present
Moved Ymacs support into separate content script

Also fixed a bunch of typos.
Factored out content script sandbox-facing code
Fixed an error introduced in 33d2bfc7ac8a2f107765061a2e62ffef2d087825
Simplified Ymacs content script
Nuke sandboxes after injecting content scripts

Also opt debug builds out of content script caching.
Moved iCloud support to separate content script

Unfortunately, this content script can’t operate in strict mode because the page scripts use a deprecated API that’s unavailable in safe mode.