refactor server_plugins.php:
1. change HTML mixture to php
2. change long code to functions
3. move functions to libraries/server_plugins.lib.php
fix code indention
using space instead of Tab
move PMA_getSubPageHeader to server_common.inc.php
fix the issues:
1. replace tab with space in server_bin_log.lib.php
2. move $bin_log to server_binlog.php
3. add server common function file server_common.lib.php
Merge pull request #405 from xmujay/0604_server_plugins

refactor server_plugins.php: