Added definitions for Handlebars Runtime

User has to declare var `Handlebars` as either `HandlebarsStatic` or `HandlebarsRuntimeStatic` (one or the other, as you cannot have both of them in same app)
    - `HandlebarsStatic` is handlebars with template compiler
    - `HandlebarsRuntimeStatic` is handlebars runtime with no compiler (for when templates are pre-compiled at the server side)