Removed Tabs
Added Logging to find GDI+ ExternalException (0x80004005).

Renderer:
 - Avoided Font to return zero
 - Dispose also the stringFormat on Dispose

ColumnModel:
 - Dispose also disposes all known renderers
 - Use dictionary instead of Hashtable

Table:
 - call base.OnPaint to issue events

CellRenderer:
 - DrawString: added more information to thrown exception

Investiagetd Exception:

Method 'CheckErrorStatus' in type 'Graphics' : ExternalException : A generic error occurred in GDI+.
System.Runtime.InteropServices.ExternalException (0x80004005): A generic error occurred in GDI+.
   at System.Drawing.Graphics.CheckErrorStatus(Int32 status)
   at System.Drawing.Graphics.DrawString(String s, Font font, Brush brush, RectangleF layoutRectangle, StringFormat format)
   at XPTable.Renderers.CellRenderer.DrawString(Graphics graphics, String s, Font font, Brush brush, RectangleF layoutRectangle, Boolean canWrap) in S:\xptable\xptable_git\Renderers\CellRenderer.cs:line 161
   at XPTable.Renderers.TextCellRenderer.OnPaint(PaintCellEventArgs e) in S:\xptable\xptable_git\Renderers\TextCellRenderer.cs:line 122
   at XPTable.Renderers.CellRenderer.OnPaintCell(PaintCellEventArgs e) in S:\xptable\xptable_git\Renderers\CellRenderer.cs:line 572
   at XPTable.Models.Table.OnPaintCell(PaintEventArgs e, Int32 row, Int32 column, Rectangle cellRect) in S:\xptable\xptable_git\Models\Table.cs:line 7849
   at XPTable.Models.Table.OnPaintRow(PaintEventArgs e, Int32 row, Rectangle rowRect) in S:\xptable\xptable_git\Models\Table.cs:line 8508
   at XPTable.Models.Table.OnPaintRows(PaintEventArgs e) in S:\xptable\xptable_git\Models\Table.cs:line 8426
   at XPTable.Models.Table.OnPaint(PaintEventArgs e) in S:\xptable\xptable_git\Models\Table.cs:line 7601
   at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
   at System.Windows.Forms.Control.WmPaint(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)