Move built-in functions to separate modules

partial-blueprint function-plugins

Change-Id: I6ee08f962935c07d292ab4f3f298fbb5e5176e8f
Remove Fn::FindInMap from HOT

Since HOT doesn't include a Mappings section, this function can't ever do
anything useful.

Change-Id: I669b5516e13927f2b9d28f15dd2d728f27fd4a43
Merge "Move built-in functions to separate modules"
Merge "Remove Fn::FindInMap from HOT"