Add method for users to make changes to the nginx configuration

[ezwang]

Allow users to use certain nginx commands to change variables such as the max upload size, serving from static directories, etc.

[ezwang]

This could be done by either making a parser to validate a user submitted nginx configuration, or making a model system for simple operations (static folders, redirects, etc.) and writing that out to a nginx configuration.

The latter option would be better if any changes need to be made to the default configuration, but would provide less flexibility for users.