UI: confirm Chroma is operational

The documentation for the [chroma fingerprinting plugin](http://beets.readthedocs.org/en/v1.3.7/plugins/chroma.html) specifically warns the user that it's tricky to set up and may not work correctly:

> First, it can be trickier to set up than beets itself (you need to set up the native fingerprinting library, whereas all of the beets core is written in pure Python).

The complexity of the dependencies section which follows suggests this as well, and [issue 885](https://github.com/sampsyo/beets/issues/885) warns me that the solution to it may also break chroma (or so I infer from the solution being to remove one version of the library when somone writes "We've seen some hangs when using both versions simultaneously, as can happen when the chroma plugin is also enabled.")

But while importing, there is no indication of whether the fingerprinting is working or if one is spending many hours doing tagging while crippled! A simple startup message like 'checking fingerprinting is working... fingerprinting seems to be working' would suffice.

(I've discovered that my chroma fingerprinting _does_ seem to be working when I turn on debugging output like `beet -v import` but this is (1) not something users will think to do, and (2) makes the import interface much harder to use.)

Start with the chroma fingerprinting plugin and compare a normal `beet import` with `beet -v import`, tracing where fingerprinting setup begins. Done means a normal import clearly reports whether fingerprinting is operational without requiring debug output, while preserving the existing import workflow.

Written by the indexing model from the issue text.