Components: md-prefix and md-suffix selectors should be camel-cased

[PascalPrecht]

Bug, feature request, or proposal:

This is a leftover from moving from dash-cased to camel-cased directive names.

Currently it looks like this:

<md-input-container align="end">
  <input mdInput placeholder="amount">
  <span md-prefix>$&nbsp;</span>
  <span md-suffix>.00</span>
</md-input-container>

But it should be this:

<md-input-container align="end">
  <input mdInput placeholder="amount">
  <span mdPrefix>$&nbsp;</span>
  <span mdSuffix>.00</span>
</md-input-container>

[jelbourn]

We will need to support both selectors temporarily and then remove the dash-case versions in a subsequent release.

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