Overlap merge: master slave

Problem

• I'm afraid that slave may break because master FOV chain may skip some slaves because it does 1v1 FOV comparison
• when slave FOVs missed out and shifts applied to other FOVs, gaps appear.

Idea

• before matching, create master/slave/bottom groups, ensure each slave has a master, each master has a slave
• match every master that has a in-FOV, same-CC slave, match
  

imp

1. 3 runs, for each master, find slave, bottom, of same FOV.cc
1. keep a vb_has_group for master, slave, bottom
2. after 1st run, vb_has_group_master = [true, ......false, true.....], vb_has_group_slave = [true, ......true, true....], vb_has_group_bottom = [true, ......true]
   
3. in 2nd run, unpaired master(k), finds in slave[k-1, k, k+1] possible slave,
   
4. in 3nd run, same for slave(k), finds in master[k-1, k, k+1] ...