Minimize dependencies to NekoSerializer

Since I am going to provide another favour of HtmlSerializer, namely NekoCompactSerializer, I would like to let user to choose which serializer to use.

In order to make that happen, I did the following:

1. Utility methods that are common to all HTML serialization are moved to 
   HtmlSerializer.
2. GadgetHtmlParser subclasses no longer attach HtmlSerializer themselves during 
   parseDomImpl. Instead, they implement a template method createSerializer. 
   This further strengthen the contract between GadgetHtmlParser and 
   HtmlSerializer.

[cnwan, 2009-03-24 10:45:05]

repositioned to java/... instead of trunk/...

[louiscryan, 2009-03-24 16:37:10]

Looks fine to me.

http://codereview.appspot.com/27100/diff/1002/1011
File
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/HtmlSerializer.java
(right):

http://codereview.appspot.com/27100/diff/1002/1011#newcode110
Line 110: public static void printEscapedText(CharSequence text, Appendable
output) throws IOException {
FYI - We will likely be switching the serializer to use the one in Caja with the
next Caja syncup so this may not be needed. Fine for now.