Install generator needs better tests

[radar]

We just ran into an issue where the fix for #88 caused the install generator to break for new applications. It was requiring the user_class configuration option to set and was giving a non-trivial error message to users.

I think that we should have a test for the install generator which is more of an "integration" test than the current "unit" test that lives in spec/generators. This integration test should use the wonderful Aruba to create a brand new Rails application and walk through the install steps for Forem, running checks on the output of the content of the installer.

Without this, there's a chance that any change to Forem could again break the install generator, and when that happens anybody who's trying out Forem for the first time will see this and think bad things about Forem. The install generator (and the installation process) should amaze people at what it did for them and how easy it was.

Let's not break this again, ever.

Massive thanks to Aston J for pointing this out.

[radar]

There's now also #102 which is caused by problems with the way that this is being tested. Perhaps fakefs should be looked into as a possible alternative to this.

[radar]

This is fixed by #149.