Import from skbio instad of pycogent

This will depend on brokit, so wait on the merge of brokit modules that
@josenavas is working on
Removing pycogent_backports/usearch.py
Removing pycogent_backports.usearch.py
Merge pull request #1432 from adamrp/skbio_app_util

Import from skbio instad of pycogent
Use SciKit-Bio in qiime/stats.py

With these changes we replace combinate with itertools.combinations,
additionally some imports from cogent have been replaced with scikit-bio
imports.
Removing pycogent_backports/uclust.py
Removing pycogent_backports/seqprep.py and pycogent_backports/fastq_join.py
removing pycogent_backports/(blat,rdp_classifier).py
removing pycogent_backports/(bwa,mothur).py
Update setup.py to install brokit
Deleting tests for the application controllers of blat and bwa
Remove unused imports of unzip

This function was not being used anywhere in these modules.
Fixing imports to brokit
Merge branch 'master' of git://github.com/qiime/qiime into brokit
Fix non-pythonic iterations
Merge pull request #1437 from ElDeveloper/remove-unzip-usage

Remove unused imports of unzip
Merge pull request #1436 from ElDeveloper/remove-combinate

Use SciKit-Bio in qiime/stats.py
Merge pull request #1438 from josenavas/brokit

Port pycogent backports application controllers to brokit
Solving merge conflicts
Fixing @wasade's comments