Include LICENSE file in repository

[ncalexan]

As part of publishing #199, I'm saying that the Logins API is Apache 2. Is this whole repo Apache 2? MPL?

[vladikoff]

We should MPL-2.0 unless we cannot MPL-2.0 for some reason

[rfk]

From mtg: copy what the android-components repo is doing == MPL

Also need to grep for Apache-licence headers to ensure consistency.