Show Home "Take a tour" only after dismissing "Help Center"

#4680 

##### Ready for review

#### Changes

* Code cleanup in "Help Center" page callback
* Dismissing the help center displays the "Home" tour
* **Note**: There is no expire condition yet-- multiple reloads & dismissals result in the tour returning.

#### Todo (maybe?)

* Save timestamp when a user closes the Help Center-- don't show the tour ever again once recorded.