Add dynamic instructions for portlet rating.

Reflects whether user has already rated.  In marketplace entry page and in pervasive rating modal.

Screenshots
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Adds dynamic instructions about rating to the Marketplace entry page, reflecting when a portlet is not yet rated:

![entry_page_not_yet_rated](https://f.cloud.github.com/assets/952283/2529141/7a5bce0e-b517-11e3-992a-e3a0d5e97586.png)

or is just now rated:

![entry_page_just_now_rated](https://f.cloud.github.com/assets/952283/2529140/73f2e2d2-b517-11e3-95ca-f7572957959f.png)

or was previously rated:

![entry_page_already_rated](https://f.cloud.github.com/assets/952283/2529138/6c0a48da-b517-11e3-987e-bd4937717973.png)

These same messages are also presented in the inline rating modal, again reflecting not yet rated:

![modal_not_yet_rated](https://f.cloud.github.com/assets/952283/2529128/6474ee90-b517-11e3-82ab-5c2ee0a0f53a.png)

or already rated:

![modal_already_rated](https://f.cloud.github.com/assets/952283/2529121/5d991d3a-b517-11e3-9243-4495db76ff5d.png)

Implementation notes
==================

* Messages in message bundle.

Known issues and technical debt
============================

Messages not localized to non-English
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While instruction messages are externalized into `Messages.properties`, they're not localized to and included in the non-English bundles.

Instructions do not include number of stars
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Doesn't address including the actual number of stars in the instructions message when the portlet was already rated or is just-now rated.  Implementing that will probably require retaining a placeholder or addressable `<span/>` in the message at runtime to allow punching in the number of stars from JavaScript.

Something is goofy about Marketplace entry page labels
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![9037480f1b48a5a3ffe9a09fe77158a9079a9e04ef](https://f.cloud.github.com/assets/952283/2529064/b2749970-b516-11e3-8470-225e4a1b7591.png)

possibly arising from a mis-merge in a rebase of this `marketplace` branch?

Anyway, this pull request doesn't address that.