fix(toolbar): prevent content overflow and line-wrapping

[devversion]

• No longer wraps lines inside of a md-toolbar-row
• Overflow for X-axis and Y-Axis are now hidden. Developers should use multiple md-toolbar-row elements or can always overwrite the styles.

Note: An ellipsis for flex elements is definitely possible, but it just bloats the toolbar and needs some refactoring. We should revisit this with #1718

Fixes #2451

[crisbeto]

There's a md-truncate-line mixin for these cases.

[devversion]

True, but this also tries to show an ellipsis, which doesn't work and is then unnecessary.

[jelbourn]

LGTM

[mmalerba]

I'm seeing some test failures when I try to merge this into Google's codebase:

1. The white-space: nowrap seems to affect the children of md-toolbar-row as well. I think flex-wrap: nowrap might work better in this case.

2. One team has an absolutely positioned popup when you hover over a button in the md-toolbar-row, the overflow: hidden here doesn't play nice with that. Is there some way we can avoid it?

[devversion]

As discussed with @mmalerba. We are just doing white-space: none for now because having overflow: hidden might reduce flexibility for toolbar elements.

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