修改数据库 论文增加点击量和时间字段
首页最新和最热文章能正常显示了
论文详情页，关键字和收藏、下载还没做

Signed-off-by: yaozhen <pop59461@126.com>
Merge branch 'master' of git@github.com:younglaker/lunwen.git

Conflicts:
	application/models/home_model.php

Signed-off-by: yaozhen <pop59461@126.com>