Rename {{> UI.*}} to Template; remove UI uses

Rename inclusion macros (with back-compat) to: Template.dynamic, Template.contentBlock, Template.elseBlock.

Update all uses and mentions of UI in the repo, unless they are there for back-compat or testing reasons.

To do: Run unit tests.  Update docs for UI.dynamic.  Document Template.contentBlock and Template.elseBlock.
Back-compat tests
Ban templates named after macros like “dynamic”
Fix presumed typo in jsdoc.sh
Rename UI.dynamic to Template.dynamic in docs
Merge branch 'deprecate-ui' into devel