ENH: Add find_repeated to qiita_db.util & tests
API: Format exception with duplicated header names
BUG: Catch error and format it properly

QiitaDuplicateHeaderError was not being caught and thus was not showing
any message via the GUI.

Fixex #648
BUG: Format errors properly
STY: Add extra space
Merge branch 'master' of git://github.com/biocore/qiita into issue-648

Conflicts:
	qiita_db/metadata_template.py
Merge branch 'master' of git://github.com/biocore/qiita into issue-648
Merge pull request #653 from ElDeveloper/issue-648

BUG: Show error message with duplicated headers