Autolink in project/group description

Group:

![Screenshot 2014-06-12 22.58.07](https://dev.gitlab.org/uploads/dzaporozhets/gitlabhq/b5a95eff8a/Screenshot_2014-06-12_22.58.07.png)

Project:

![Screenshot 2014-06-12 22.58.36](https://dev.gitlab.org/uploads/dzaporozhets/gitlabhq/51e516fb41/Screenshot_2014-06-12_22.58.36.png)

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Fixes http://feedback.gitlab.com/forums/176466-general/suggestions/4110570-group-description-should-support-markdown