Improve document loading and position iteration speeds

This patch is focused around improving the performance of some of the really tight loops in WebODF. 

I've uploaded another document (king james bible from Project Gutenberg) to this url as another test case: https://drive.google.com/file/d/0B1EH5OPb-RrjckZ2MDRDNzlFVUk/edit?usp=sharing

The results of this patch on the main results (tested in Chrome, Safari & FF) are roughly:
Using the 100pages.odt doc:
Open document - 20% faster
Move to document end - 30% faster

Using the 1000pages.odt doc:
Open document - 30% faster
Move to document end - 160% faster

Using the KingJamesBible.odt doc:
Open document - 40% faster
Move to document end - 3000% faster (no, really... 2mins down to 6.7s)