Operation.transform: need at least basic support for full OT

[iclems]

Otherwise it crashes if some users gets offline and online again while another one is still editing.

[iclems]

Transform takes two operations A and B that happened concurrently and produces two operations A' and B' (in an array) such that apply(apply(S, A), B') = apply(apply(S, B), A'). This function is the heart of OT.

lib/operation.js should provide Operation.transform(a,b)

[iclems]

For now, I've basically disabled transform by returning directly the ops. It should work for cases where no conflicting command (insert, delete row, ...) was used. Needs testing nevertheless as I've seen the first operation missing after working offline for some time.

[iclems]

@audreyt message about OT support:

In practice, we've found OT not really necessary for the majority of spreadsheet operations, as they tend to be commutative set commands.

For the few commands that do cause conflicts (e.g. insertrow), it might still be simpler to use the timestamp to tiebreak into a undo-replay sequence, as depicted in http://www.aosabook.org/en/socialcalc.html#fig.soc.resolve (not yet implemented in EtherCalc).