- use list to show bmap encoding settings, instead of user input raw string. it will give a more obvisous interface.
* add bmap encoding setting properties in ptrprop_resolver.
* update ptrprop_resolver for more clear usage.
- following features has not been implemented yet.
* default value for bmap encoding list.
* the bridge function in ioport_shared module (filter empty item in result)
* validate encoding list result when importing and exporting virtools file.