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[shepmaster]

Spawned from #184.

This should probably include the Rust version as well, since it can be decoupled from what's in the nightly.

[lqd]

For anyone wanting to pick this up, here's some more information.

There's the rustfmt -V option to return its version, in a format very similar to rustc -V, for example 0.3.6-nightly (e0e3e22 2018-01-18). (I wasn't able to try with clippy at this point)

Adding support for this could be similar to how the playground gets the channels' rustc version.

For example, for the server-side backend, the stable version endpoint is here, and the code asking rustc for its version on a given channel, and parses the results into its components is here.

Client-side, there are different routes defining the previously mentioned endpoints. These are used in the performVersionsLoad function here, which is called when the app starts up, ultimately storing the resulting versions in the app state here. The UI reads these versions here in the component displaying them, via these selectors.