sstables: convert collections to mutation
sstables: convert collections to mutation

We do our best to avoid serializing every cell we see. We will accumulate them
all in an internal data structure, and then finally serialize it to our internal
format all at the same time.

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@cloudius-systems.com>

stamhe/scylla,asias/scylla,dwdm/scylla,acbellini/scylla,kjniemi/scylla,dwdm/scylla,linearregression/scylla,capturePointer/scylla,kjniemi/scylla,justintung/scylla,bowlofstew/scylla,avikivity/scylla,aruanruan/scylla,glommer/scylla,tempbottle/scylla,phonkee/scylla,duarten/scylla,shaunstanislaus/scylla,scylladb/scylla,asias/scylla,eklitzke/scylla,glommer/scylla,senseb/scylla,phonkee/scylla,shaunstanislaus/scylla,victorbriz/scylla,kjniemi/scylla,stamhe/scylla,acbellini/scylla,linearregression/scylla,aruanruan/scylla,senseb/scylla,acbellini/scylla,respu/scylla,wildinto/scylla,avikivity/scylla,gwicke/scylla,raphaelsc/scylla,aruanruan/scylla,guiquanz/scylla,capturePointer/scylla,eklitzke/scylla,duarten/scylla,shaunstanislaus/scylla,avikivity/scylla,rluta/scylla,kangkot/scylla,rentongzhang/scylla,scylladb/scylla,scylladb/scylla,victorbriz/scylla,scylladb/scylla,capturePointer/scylla,gwicke/scylla,victorbriz/scylla,duarten/scylla,stamhe/scylla,justintung/scylla,kangkot/scylla,wildinto/scylla,respu/scylla,senseb/scylla,phonkee/scylla,glommer/scylla,eklitzke/scylla,dwdm/scylla,guiquanz/scylla,gwicke/scylla,tempbottle/scylla,linearregression/scylla,tempbottle/scylla,rentongzhang/scylla,respu/scylla,kangkot/scylla,bowlofstew/scylla,asias/scylla,rluta/scylla,rluta/scylla,bowlofstew/scylla,rentongzhang/scylla,wildinto/scylla,justintung/scylla,guiquanz/scylla,raphaelsc/scylla,raphaelsc/scylla