Adding ability to convert reference FASTA files for nucleotide sequences

Added converter, and modified ADAM FASTA record to a more generic ADAMNucleotideContig record. This adds a command which allows for text FASTA files to be imported into ADAM; specifically, we support an _expansion_ of the FASTA standard, where multiple FASTA files that include the name of the contig they specify can be concatenated into a file. Additionally, we allow the referenceIds of sequences from a FASTA to be rewritten to correspond with the referenceIds present in a current read file.