Android / Java installation instructions

[mattheworiordan]

@piotrekinventica the Java / Android installation instructions have changed unfortunately which needs a small update on your side please for ALL Java & Android demos.

Please see ably/docs#213 and ably/docs#196 once the PR is merged and ensure all changes are reflected.

Also, please confirm if your PRs at https://github.com/ably/docs/pulls can be closed or still need to be merged in. I would like to ensure all work outstanding is merged in in full and we can close this work.

[mattheworiordan]

Please note too that the Android demo has invalid image references such as /images/tutorials/token-authentication-android-anonymous.png, the image was not part of https://github.com/ably/docs/pull/183/files. Please do a PR on docs as well to fix that.