Upgrade to latest KOstache module

This has required some changes to our view class structure as well,
due to the new Renderer Engines that KOstache implements. In reality
the amount of work that will be required to migrate sites over to this
new system should be small.

The main change is that View_Template_{Admin,Main} have been renamed to
View_Layout_{Main,Layout}, so all view classes will need to be updated.

Views that were once standalone can no longer call the "render" method
on the view class, as view classes are now dumb and plain old PHP
objects. Instead they will have to do the following:

  $foo = Kostache::factory()->render(new View_Foo);

Partials are now automatic, so no need to explicitly define them in the
class. Refer to the KOstache documentation for details
Move g_eventmsgs logic into OZ_View_Layout, instead of OZ_Controller

The event messages will only be cleared if g_eventmsgs gets used in a
template.