修改Liferay中用户的默认头像
这小东西不好找，找了半天，结果是在portal.properties配置文件中定义，这个文件是在源码中的。可以在扩展工程中或者直接在jar中替换掉。
#
# Set the location of the default user portrait image that is used for
# missing user portrait images. This image must be found in the class path.
#
image.default.user.portrait=com/liferay/portal/dependencies/user_portrait.gif
同时也可以指定默认Logon：
#
# Set the location of the default company logo image that is used for
# missing company logo images. This image must be found in the class path.
#
image.default.company.logo=com/liferay/portal/dependencies/company_logo.png
