refinements in pageman
* refactor pageman.go a bit, move some functionalities to a new Page struct, not putting everythin gin PageManager anymore
* PageData is now called PageCtrl instead, and has a "SetTitle" method
refactor the bind engine, create "scope" object for managing helper
functions and model fields, can now call a method of the model
New proper interface for binders; TodoMVC's Delete now working.

* Change the base interface for binders, now pass a data struct to the
binder methods instead of a bunch of arguments.
* Clean interface with the methods for the binders to do things, thus we
hide implementation details
* With the new things at hand, TodoMVC's Delete is now implemented with
a simple "pass in" model
binder functions instead of a bunch of arguments.
outputs of bind-each can now be used in following binds