#200: bind server-side vars to ${Hole}s

Fixes #200.

Before this PR, a server-side var such as this:

<input ws-var="MyVar" />

would be rendered as something like this:

<input oninput="some-generated-function-name(&quot;some-guid&quot;, &quot;MyVar&quot;)(this)(event)" />

This PR does the following:

Render the above as this instead:
```
<input ws-var="some-guid::MyVar" />
```
Serialize the template in <meta> and have its pre-initialization create the client-side Vars, find the above ws-vars and bind them. Also make these holes available globally to RunFullDocTemplate as some-guid::MyVar.
Render ${MyVar} text holes as ${some-guid::MyVar}, so that it gets picked up by RunFullDocTemplate.
During post-initialization, call RunFullDocTemplate. This populates all the ${some-guid::MyVar}s, unless that was already done by the user calling a template's .Bind() (which calls RunFullDocTemplate) during initialization (eg in a Web.Control).

dotnet-websharper / ui