Update nginx configurations and php.ini to increase maximum file size.

[taheralfayad]

Fixes #942. In this current iteration of UDOIT, the maximum file size that the user is allowed to upload to a course is 1MB, which renders the file replacement modal useless for most PDFs. What currently happens when you try to upload a file that is >1MB is that UDOIT returns an unhandled 413 error, which isn't really that informative to the user. To combat that, I set the acceptable upload file size to 10MB in the nginx configurations for local.conf and deploy.conf. I also set upload_max_filesize and post_max_size to be 10MB in php-custom.ini.

[dmols]

Left a comment on a possible wording change, but otherwise, the changes look great! I'm able to upload files of up to <10mb and see the error modal pop up when I input a file of size >10mb. Good to push.

[dmols]

Changes requested were made. Good to push!