Misc:
- Remove annoying message when convert TxDB
- Check crisprbe for all strand configuration

PairedGuideSet
- Modify getter functions
- Create a findPairedSpacers function.


# Done:
addSNPAnnotation.R
addOnTargetScores.R
addPamScores.R  
addCrispraiScores.R 
addRestrictionEnzymes.R
addSequenceFeatures.R  
addRepeats.R
addGeneAnnotation.R
addTssAnnotation.R    
addOffTargetScores.R

# Not done       
addSpacerAlignments.R


