Remove Function(...) in component OO due to CSP

Can't use what's effectively an "eval" and still be safe for restrictive Content Security Policies.  Hopefully we get a better way to make classes print nicely in the dev console in the future.
Add UI.renderWithData; test UI.{insert,render*}
Spacebars: Disallow non-initial `this` in paths

Apparently `../this` used to work as a synonym for `..` in Handlebars, but in Spacebars it actually would look for a property named `this`, which caused confusing breaking changes in apps.
Change {{> content}} to {{> UI.contentBlock}}

...and elseContent to UI.elseBlock.
Move toHTML to ui package

toHTML/toText will be Blaze functions.  HTMLjs gets smaller; it's just a syntax library with constructor functions, and any code that consumes HTMLjs trees can decide what objects are legal in it.  Having a version of toHTML that doesn't know about Blaze just seems like extra code right now.
Create blaze-tools package with JS code gen utils

This will be the part of Blaze that is needed at compile time by template compilers like Spacebars.