Added new face type : head

Now you can replace the head.
Example: https://www.youtube.com/watch?v=xr5FHd0AdlQ
Requirements:
	Post processing skill in Adobe After Effects or Davinci Resolve.
Usage:
1)	Find suitable dst footage with the monotonous background behind head
2)	Use “extract head” script
3)	Gather rich src headset from only one scene (same color and haircut)
4)	Mask whole head for src and dst using XSeg editor
5)	Train XSeg
6)	Apply trained XSeg mask for src and dst headsets
7)	Train SAEHD using ‘head’ face_type as regular deepfake model with DF archi. You can use pretrained model for head. Minimum recommended resolution for head is 224.
8)	Extract multiple tracks, using Merger:
a.	Raw-rgb
b.	XSeg-prd mask
c.	XSeg-dst mask
9)	Using AAE or DavinciResolve, do:
a.	Hide source head using XSeg-prd mask: content-aware-fill, clone-stamp, background retraction, or other technique
b.	Overlay new head using XSeg-dst mask

Warning: Head faceset can be used for whole_face or less types of training only with XSeg masking.

XSegEditor: added button ‘view trained XSeg mask’, so you can see which frames should be masked to improve mask quality.

XSegEditor/QStringDB.py

@@ -30,6 +30,11 @@ class QStringDB():
                                                 'zh' : '查看遮罩通道',
                                            }[lang]
                                            
+        QStringDB.btn_view_xseg_mask_tip =  {   'en' : 'View trained XSeg mask',
+                                                'ru' : 'Посмотреть тренированную XSeg маску',
+                                                'zh' : '查看导入后的XSeg遮罩',
+                                            }[lang]
+                                           
         QStringDB.btn_poly_type_include_tip = { 'en' : 'Poly include mode',
                                                 'ru' : 'Режим полигонов - включение',
                                                 'zh' : '包含选区模式',