Extract gene information

[dhimmel]

Closes https://github.com/cognoma/cancer-data/issues/23

This downloads the latest Entrez Gene information from their FTP site (updated daily). Obsoleted genes have missing values for the columns from Entrez Gene. Unclear how we want to proceed wrt making the backing/django-genes and cancer-data use the same gene data.

[dhimmel]

Here's the head of genes.tsv, which would become part of the Cognoma data release:

entrez_gene_id	symbol	description	chromosome	gene_type	synonyms	aliases	n_mutations	mutation_frequency	mean_expression	mutation	expression
1	A1BG	alpha-1-B glycoprotein	19	protein-coding	A1B	ABG	GAB	HYST2477	alpha-1B-glycoprotein	HEL-S-163pA	epididymis secretory sperm binding protein Li 163pA	30	0.004106	6.71	1	1
2	A2M	alpha-2-macroglobulin	12	protein-coding	A2MD	CPAMD5	FWP007	S863-7	alpha-2-macroglobulin	C3 and PZP-like alpha-2-macroglobulin domain-containing protein 5	alpha-2-M	130	0.01779	13.34	1	1
3	A2MP1	alpha-2-macroglobulin pseudogene 1	12	pseudo	A2MP	pregnancy-zone protein pseudogene	4	0.0005475		1	0
9	NAT1	N-acetyltransferase 1	8	protein-coding	AAC1	MNAT	NAT-1	NATI	arylamine N-acetyltransferase 1	N-acetyltransferase 1 (arylamine N-acetyltransferase)	N-acetyltransferase type 1	arylamide acetylase 1	monomorphic arylamine N-acetyltransferase	17	0.002327	6.729	1	1
10	NAT2	N-acetyltransferase 2	8	protein-coding	AAC2	NAT-2	PNAT	arylamine N-acetyltransferase 2	N-acetyltransferase 2 (arylamine N-acetyltransferase)	N-acetyltransferase type 2	arylamide acetylase 2	26	0.003559	2.086	1	1

[dhimmel]

Do not review yet --- will update in the wake of https://github.com/cognoma/genes/pull/1.