DBManager, getFromCache: fix raising of error
BasModel, updateAppRepr : fix handling of empty string
VolumeGroup: fix default values for ModelObject
VolumeDAO_parse: fix paring of Parameterlist
CellService, getCellInfo: self.getFileServers returns

list of hostnames, not objects
FileServerDAO_parse, getPartList : add comment about return value
VolService, OSDService: saniti\e code a bit, nothing exciting
BaseDaO: some small cleanup
VolGroup: Remove it from DB and DAO.

in Service:
- get Info from DB by a join
- call getVolume from separate "vos"-calls
Mdel Project: fix defaults
DB: add new Table and Modelobject ProjectSpread

which contains the spread of volumes belonging to a project
this is expensive to calculate, so have a helper table for this.
LookupUtil: multiple fixes

use DBManager methods,
fix defaults
DBManager: make sure Objects are expunged from sqlalchemy

session
CellService, FsService: make interface more consistent

CellService only returns names of fileservers, nothing more.
ProjectService:  add first implementations of

Volume services