Eliminate static methods from ContentFilterToadlet

Use a RedirectException in QueueToadlet instead of calling
ContentFilterToadlet directly. Also clean up ContentFilterToadlet
code.
Some javadocs for toadlets
Add handleMethodGET as an actual abstract method. Almost all toadlets are likely to need this, and it makes the code clearer.
Factor out callToadletMethod()
Short-cut the common case (GET request)
Javadocs for handleMethodGET
Javadocs. ctx can be null.
Merge remote-tracking branch 'vwoodzell/filter-toadlet-cleanup' into web-interface
Merge branch 'web-interface-and-filter-toadlet-fixes' into stable-1448-new