Allow the user to assign the config file.

First, if the command line offers the option, '--config-file PATH',
assign 'PATH' to beego.AppConfigPath; or, use the environment
'BEEGO_APP_CONFIG_FILE'. If neither exists, use beego's default value.

In the config file, the user maybe define 'ViewsPath' and 'StaticDir'.
Default, they use the 'views' and 'static' in the current directory.
Merge branch 'master' into xgfone
Modify 'line-height' of the article and the ueditor to 1.8px