Set the encoding of Storm UI to UTF-8

storm UI imports the jquery-tablesorter project, in which there're codes as below:
```
return /^[£$€?.]/.test(s);
```
original source code:
https://github.com/christianbach/tablesorter/blob/master/jquery.tablesorter.js?#L910

These special characters will bring problems for some encoding, e.g GBK.
The topology summary will not display normally.
Better force the encoding to UTF-8.