Update docs/dev_guide/intro/mojito_mvc.rst
Cleaned up logging example.
Adding new documentation for configuring YUI in Mojito.
Finished first draft of documentation.
Added section IDs, edited, added table of properties for 'app' object.
Fixed an issue with the H1 level heading.
Made changes suggested by Caridy and some edits.
Added paragraph mentioning that language versions of app_loader are auto-generated by Mojito if language versions exist.
Added YUI config doc to index.rst and edited the YUI config doc.
Replaced relative path to API docs w/ absolute URLs for those viewing docs on GH.
Merge pull request #891 from jianlin/patch-3

Update docs/dev_guide/intro/mojito_mvc.rst
Merge pull request #892 from zhouyaoji/docs_yui_config

[doc] Documentation for how to configure YUI for Mojito applications. 
Update docs/dev_guide/intro/mojito_mvc.rst
Merge pull request #893 from jianlin/patch-4

Update docs/dev_guide/intro/mojito_mvc.rst