[sugar] All activities should switch to a primary toolbar tab

[Eben Eliason]

Though this isn't in the guidelines formally yet, we are strongly
recommending that activities switch to a "primary" tab when launched.
For instance, Write should focus the "Text" toolbar; Paint should
focus the "Tools" toolbar; Record should focus the "Photo" toolbar;
etc.

In other words, whatever you consider to be the base set of tools
needed to dive in to your activity you should expose up front,
eliminating the need for the kids to manually switch tabs before
exploring your activities.  There is an API for switching tabs (as
tabs should also switch automatically according to context, when
appropriate), which can be used to accomplish this goal.

Thanks for taking the time to do this!  (And if you don't, we'll hunt
you down at a later date with individualized bugs in trac.  Consider
yourself warned!)

- Eben