Rewrite get_qiime_scripts_dir

Now runs the equivalent of 'which print_qiime_config.py' to infer the scripts directory.
update util.py modules, update some unit tests
update print_qiime_config.py and parallel scripts
update workflow library code
update denoiser code and add qiime.util.which

qiime.util.which is now my favorite python function
remove remaining refs to python_exe_fp
Update docs with config file changes
remove cloud_environment from QIIME
Remove working_dir from QIIME

temp_dir (in QIIME config) is now used in place of working_dir (should only affect some pieces of parallel QIIME).
Remove poller_example.py

This has been slated for removal for awhile... it's time
remove poller_fp option lookup

not being used anywhere
Merge pull request #1342 from jrrideout/issue-1338

Remove qiime_scripts_dir and python_exe_fp