Focus manager: don't require id's on widgets.
This changes activeStack to contain widgets rather than widget ids.
I updated the test but I can't actually run it, since it still referencing
old dijit widgets.  It also needs to be converted to Intern.
Get KeyNav tabIndex working.

Don't put tabIndex in the KeyNav prototype.  It triggers Stateful to create a custom
tabIndex setter which then triggers Widget#enteredViewCallback to
call the setter on widget startup.  We don't want any of these things to happen.
Rather, the app should be able to set/change tabIndex on the element (i.e. widget
root node) without any interference/action from delite.

The only thing that we really need to do is to set tabIndex to 0 if it was not
specified explicitly by the app.

Fixes #62.
Proper KeyNav tests.

- test letter key search
- test left, right, home, and end key callbacks
- test programmatic creation
- test childSelector as string and as function
get it working on IE
remove dynamic tabindex change test