docs(readme): update stuff planned for Q1 2018

[donroyco]

Bug, feature request, or proposal:

Proposal

What is the expected behavior?

Up to date content in readme file.

What is the current behavior?

The current README.md on master has the 'High level stuff planned for Q4 2017 (October - December)' and should be updated to Quarter 1 of 2018.

What are the steps to reproduce?

Just visit the https://github.com/angular/material2 and read the Project status.

What is the use-case or motivation for changing an existing behavior?

Keeping people up to date with the plan(s) of adding or updating features.

Is there anything else we should know?

Happy New Year! 🎆

[benb7760]

related #8942 with PR #8966

[josephperrott]

Closed by #9315

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