Add support for per-task compilation buffers within a project

[acmorrow]

The per-project compilation buffer feature (projectile-per-project-compilation-buffer) is great, but even within a project I'd like to retain the compilation buffers for different tasks (e.g. the buffer for projectile-compile-project vs the buffer for projectile-test-project). Currently all runs of projectile--run-project-cmd within a project share a compilation buffer, so when you run projectile-test-project your projectile-compile-project output is lost, and vice versa. Unfortunately, this doesn't seem possible right now since the "role" for which a given call to projectile--run-project-cmd is in play is not available. This might be a little tricky to do, since the projectile-compilation-buffer-name is invoked indirectly by compile, so the information about what role was selected will need to be retained in some way such that projectile-compilation-buffer-name can subsequently access it.