Deprecate or remove ons-template

[emccorson]

ons-template should not be used. Instead the native template tag should be used.

We have experienced problems with users using ons-template where the fix is to switch to template.

Suggested fixes:

1. Remove ons-template entirely.
2. Keep ons-template but make it only render a native template.

My preference is for 2. as it will avoid a breaking change, but if ons-template has its own specific behaviour we may need to warn users that this is changing.

We should also update the documentation to make it clearer that ons-template is deprecated.