[FileSystem] Major fixes on API

Initially the path and fullpath were wrong, after some tests on WRT
we solve this problem. This patch also fixes exceptions in general.

Example:
          _________fullPath_________
         |                          |
__kPath__________path__________name_
|        |                  |       |
/opt/usr/documents/parentdir/file.txt
|______________realPath_____________|

obs: just in the realpath, the first char of the virtual root dir
name is uppercase. (Documents, Downloads etc)

virtual root dir (documents):
   path:     documents
   fullPath: documents
   name:     ""
   realpath: /opt/usr/Documents

parentdir:
   path:     documents/
   fullPath: documents/parentdir
   name:     parentdir
   realpath: /opt/usr/Documents/parentdir

file.txt:
   path: documents/parentdir/
   fullPath: documents/parentdir/file.txt
   name: file.txt
   realpath: /opt/usr/Documents/parentdir/file.txt