ZCS4.5.4 Simplified Chinese Translation, Web client part

Hi,

It's my first time to do some contribution here:D

I did the translation based on nxzwt's work, revised some and added some which are new in 4.5.4.

Don't forget to use native2ascii first:
native2ascii --encoding=gbk \
ZmMsg_zh_CN.properties.txt ZmMsg_zh_CN.properties

Forget to say, I will be working on shortcut keys soon.

我写了一个简单的界面汉化说明，来这里看。