[TwigBridge] Replace default list style to icon
minor #12164 [TwigBridge] Replace default list style to icon (Macsch15)

This PR was merged into the 2.6-dev branch.

Discussion
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[TwigBridge] Replace default list style to icon

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Replaces default list style in **bootstrap_3_layout.html.twig** to icon.
Requires Glyphicons from Bootstrap 3.

Before:
![2014-10-07 11-55-50](https://cloud.githubusercontent.com/assets/1592053/4540807/d6f8eb46-4e0b-11e4-82bf-77b56fd1d17c.png)

After:
![2014-10-07 11-55-07](https://cloud.githubusercontent.com/assets/1592053/4540810/e02fe048-4e0b-11e4-9f3b-69902c0ae32b.png)

Commits
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9a0b2cc [TwigBridge] Replace default list style to icon