[dev] Disable sidebar by default

[Chuck Hagenbuch]

Quoting Michael M Slusarz <slusarz at horde.org>:

> The new sidebar code is good now that we got rid of frames.  But it  
> is bad because it has to be regenerated every time a page is loaded.  
>  This is quite a bit of extra load.  Enough so that I wonder if  
> sidebar should be disabled by default.  Alternatively, we need to do  
> some sort of caching of the tree so that it does not need to be  
> rebuilt on every page click.  Maybe do absolute time caching (e.g.  
> we only rebuild the tree every 'refresh_time' minutes - when the  
> page is loaded, the next refresh will be the difference between the  
> next refresh time and the current time).

That would lose us the realtime message count updates, but maybe  
certain aspects could be more dynamic than others.

I agree with Jan that it shouldn't be disabled by default.

-chuck