Modification to biom_calc and test_biom_calc and addition of test_otu_calc scripts

- Modified raw_abundance to get raw abundances for OTUID's and SampleID's based on user input. Also, added transform_raw_abundance() function to perform mathematical operations on raw abundance values obtained from raw_abundance() output.
- Changed testing for raw_abundance and transform_raw_abundance to accommodate changes to biom_calc functions.
- Created test_otu_calc.py file which automates tests for validation of otu_calc file calculations.