"Blur" filters in Hybrid

[Selur]

After I spend hours implementing this, you post this now.
Send you a link to a dev version for testing which allows to:

• select the base resizer that is used for the smoothed clip
  
• select whether that resizer should be:
  • merged using a simple weight for all planes ('all') or by a weight per plane ('split')
    Also, in 'split' mode one can select whether the weights should be applied in YUV or RGB color space.
    
  • masked merged with the smoothed clip, where the mask is build using BlindDehalo3 and an edge mask on the smoothed clip.
    
  it also has an option 'Config->Internals->Handling->Do not Synth preview process priority'.
  
  Going to bed now.
  Please test this. If the BlindDehalo3 part is not useful and the simple weighted merge is enough, let me know and I'll remove it.
  
  Cu Selur
  
  Ps.: going to bed now