New update_fsl_package script

Dedicated script for updating FSL conda packages. Does not support installation of new packages at this point in time.

Also added the fslipython wrapper for $FSLDIR/bin/ipython

tests/test_update_fsl_package.py

+#!/usr/bin/env python
+
+
+import os
+import os.path as op
+import tempfile
+import subprocess as sp
+
+
+def test_update_fsl_package():
+    fsldir = os.environ['FSLDIR']
+    cmd = op.join(fsldir, 'share', 'fsl', 'sbin', 'update_fsl_package')
+    sp.run(f'{cmd} -a -d -y -e --dry-run', check=True)