Liverome: a curated database of liver cancer-related gene signatures with self-contained context information by Lee Langho, Wang Kai, Li Gang, Xie Zhi, Wang Yuli, Xu Jiangchun, Sun Shaoxian, Pocalyko David, Bhak Jong, Kim Chulhong, Lee Kee-Ho, Jang Ye, Yeom Young, Yoo Hyang-Sook, Hwang Seungwoo