Support file system shortcut in the workbench explorer

In the workbench explorer it should have support on adding new shortcut to access part of the file system. The plan at this stage is to support local file system. It can be extended to remote file system in the future since the new Eclipse File System (EFS) API is capable of doing this. The main purpose of this is to provide a way to access files outside of the user RCP workspace. For example, experimental data can be stored remotely, or NFS mounted as part of the local file system.