Bug 910313 - [Clock] Generate DOM from markup source template interpolation. r=jugglinmike r=gnarf r=djf

https://bugzilla.mozilla.org/show_bug.cgi?id=910313

- Moves Utils.Template from Messages (apps/sms) to shared/js
- Renames Utils.Template => Template
- Moves Template tests to apps/system/test/unit/ (template_test.js)
- Updates usage in Messages
    - Replace Utils.escapeHTML() with Template.escape()
    - Replace Utils.Template with Template
- Implements Template in Clock
    - Replace markup string in program code with template calls

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>