Convert multiple BLAST XML files to single tabular file (by JJ + PJC)

Based on changes by Jim Johnson for the Galaxy-P instance at
University of Minnesota, revised and merged by Peter Cock.
Refactor to avoid global blast_program and outfile

This is mostly an indentation change, git diff -w at the command line quite short.
Select columns in blastxml_to_tabular.py (by JJ + PJC)

Based on changes by Jim Johnson for the Galaxy-P instance at
University of Minnesota, revised and merged by Peter Cock.
Column selection in blastxml_to_tabular.xml (by JJ + PJC)

Based on changes by Jim Johnson for the Galaxy-P instance at
University of Minnesota, revised and merged by Peter Cock.
Pick-your-own columns tabular output for BLAST+ tools.

Note this moves the $out_format parameter inside a conditional block.

Currently this only offers the same 25 columns already available
via our extended tabular output - adding the rest is easy but the
best user interface needs a little thought...
More BLAST+ blastn test files
Test blastn XML and tabular pick-your-own column output
Be consistent about using NCBI's grammar
Column picking test for blastxml_to_tabular
Fix when nesting for column picking; include format 5 as well
Adjust pick-your-own columns option formatting
More robust parsing of column names in blastxml_to_tabular.py
Split pick-your-own column selector into standard + extended
Default to ticking the standard columns in pick-you-own mode
Mention pick-you-own columns in README file
Clarify that I am not the sole copyright holder...

Need to include the list of contributors somewhere in the documentation too.
More detailed BLASTN and BLASTP task descriptions.

Using text from http://www.ncbi.nlm.nih.gov/books/NBK1763/
gnl|BL_ORD_ID|... prefix not specific to BLAST+ 2.2.28

See also http://blastedbio.blogspot.co.uk/2013/12/blast-should-keep-its-blordid.html