many improvements

*handles case when 1 file is provided as input (vs directory)
*igonre file if file is not accessible (broken link)
only replace first instance of CHRIS_USERS

if a string is CHRIS_USERS/../../_chrisInput/CHRIS_USERS/../filename.nii
it was replaces CHRIS_USERS 2 times, therefore was not found.
show file if only one file is visible in tree
Merge branch 'master' of git://github.com/FNNDSC/chrisreloaded