Improve CSP Generation

When using CSP, the `drogon_ctl` command creates its build artifacts in the same directory as the `*.csp` files. This is quite annoying, because it pollutes a directory that is supposed to be part of the source files. For example when I have a template called `About.csp`, I get the following files as a result:

* `About.cc`
* `About.h`
* `About.so`
* `About.so.dSYM/`

As these files aren’t meant to be user-editable, I would greatly prefer to have them reside in a completely different directory.