Exit script on failed command. Plus minor changes

[mgymrek]

The main purpose of this PR is to make scripts fail when subprocess.call(cmd, shell=True) returns a non-zero exit status. In most cases it doesn't make sense for the scripts to go any further in those cases. There are a couple other minor changes:

• Add option -w to the install_dependencies.py and install_data.py scripts that allows the script to proceed even if one of the commands failes
• Add option --no-cuda to install_dependencies.py since as far as I can tell installing inn doesn't work unless CUDA is installed.
• Added a utils.py file with a helpful function for printing progress and error messages
• Fixed small typo in header of the output file in basset_sad.py which should be alt_pred rather than alt pred
• Made minor edit to docstring of the function snps_seq1 to reflect that it also outputs raw sequences.