Morris class, grouped factors, more tests

* Added groups functionality to Morris (#24) - 06ed41a
* Wrapped all the different Morris sampling methods in a class called `Morris`. - cb12326
* Added a template class called `Sample` from which all sampling methods can inherit shared methods (such as reading a parameter file, saving the sample to disk)
* Added some more tests (for test_functions) - f8c1727
* Added read_group_file to utils.  At present, you need to pass a k-by-g matrix, where each row denotes membership of group in column g. - 5cbd77f

## Use
Generating a sample is still easy from within python:
```python
sample = Morris(paramfile, samples, levels, grid_jump, group, k_optimal)
# Save the data to disk
sample.save_data(output_filename, delimiter, precision)
# Or get the sample as a numpy array
sample.get_input_sample_scaled()
# Or
sample.get_input_sample_unscaled()
```
And just as easy on the command line (and unchanged from previous versions):
```bash
python -m SALib.sample.morris -n=100 -p=SALib/tests/test_params.txt --output=foo.txt -s=123 -k=1 --group=groups.txt
```
Note the arguments `-k` and `--group` are optional.  Including them activates the respective method of sampling.

A group file can be csv, tab-delimted or whitespace delimited and should be of the format"
```
Factor1 1 0
Factor2 0 1
Factor3 0 1
```
to create two groups, of which Factor1 is a member of group 1 (column 1), and Factors 2 and 3 are members of group 2 (column 2).

## Utils

* Added tests for read file
* Added test and new procedure to read in group files
* Amended the read file procedure so that it sniffs for the type of csv file (python standard library) (#21).

## Admin

* Excluded the tests folder from coverage
* Added other exclusions of irrelevant code to `.coveragc` config file

## Remaining work

* The code for the methods of the different Morris sampling methods still resides in each of the original python files.  These could be brought into the Morris class.
* There are opportunities for sharing more code between Morris groups and Morris.  I have used numpy matrix calculations for computing Morris groups (which uses an only slightly different method to straight-up Morris), and no loops.  I've also chunked the code a fair bit to assist with testing.
* Could add checks to ensure that the group file and parameter file factor names match, as well as sense checking for numbers of groups versus number of parameters.