Set default max upload size on new networks to 50MB per file

Existing networks will still need to change their settings. We
may actually want to consider removing this option in the future
and forcing a global level.

That's probably the best answer... :)
Add .ai, .psd, .eps, .doc, .xls, .zip to default file list
Remove .midi and .mid from default file list
Add braces for code standards
Add scripting to hide upload space options from Network Settings

These are fairly global settings right now that should be changed
carefully. We'll hide them by default and then find the proper
way to display and alter the information at a later time.

This does mean that we'll need to go through existing sites and set
them all to 50MB to match the default.

We'll also need to make sure that settings saved globally will
populate everywhere.
Don't hide extra settings on global level
Setup a structure to provide global network options

Filters the pre_site_option_{option_name} value to return a global
rather than the network's individual setting. We'll do this for
those that make sense to have a global override.
Configure a default network setting for blog_upload_space of 1GB
Provide a default list of allowed upload filetypes
Allow site admins to add new users by default
Provide a default of no for notifying network admins of new users
Provide a global default for allowing registrations
Remove hacky script used to remove network settings.
Remove items from network info that are managed globally
Provide a default of no for checking max upload space
Remove another globally managed option from network info page
Merge pull request #132 from washingtonstateuniversity/update/default-options

[PR] Update handling of default network options