allow templates to be passed through with <template client></template>

templates which have a `client` attribute will be passed through to the client intact and their contents will not be processed.

```html
This will be processed: {{name}}
<template bind="{{foo}}" client>
  This will not be processed: {{name}}
  <template>
  This is a nested template, which will not be processed either.
  </template>
</template>
```