Remove assumption that project will be run on Apache webserver

[GuySartorelli]

Right now there's a built-in assumption that a Silverstripe CMS project will be run on an Apache webserver.

There are .htaccess files in recipe core, one of which gets updated based on the allowed file types.

We should remove the assumption that the project will be run on Apache. This includes ensuring any configuration is webserver-agnostic, so that developers can spin up a Silverstripe CMS project in any PHP webserver without having to add a bunch of framework-specific configuration.

Possibly related issues

• [4.0] Block access to uploaded error-\d.html files #115
• Root .htaccess doesn't get installed when using the public webroot recipe-core#50
• Silverstripe writes .htaccess files on servers running nginx silverstripe-assets#177
• Rewrite rule in base htaccess is missing [L] #241
• TinyMCE Unavailable ->web.config reset -> IIS problem silverstripe-cms#2292

Acceptance criteria

• .htaccess files are removed
• Any configuration that needs to happen is done in PHP at the earliest point possible
• At least one non-Apache webserver is tested against for at least one module's behat tests