WIXBUG:4215

Clarify all the elements that switch bitness based on
-arch/InstallerPlatform.
WIXBUG:4410

Fix MediaTemplate/@CompressionLevel.

MergeUnrealTables would normally make MediaRow rows and WixMedia rows
consistent but that happens way before MediaTemplate is processed.
Merge commit 'e9bd5bc3e836ba487865eb0cb875d196d395dd16' into bug4410a

Conflicts:
	History.md