Transactional API at client side

[sbernard31]

Bootstap operation and write composite(#959) need atomic modification of the LWM2M tree.
So maybe we need a commit/rollback mechanism or at least an API which allow user to implement it.

[sbernard31]

@moznion, do you already feel you need something like this ?

[moznion]

Yes, absolutely! Sometimes I was feeling I wish I were able to manipulate the tree atomically.

[sbernard31]

Do you already have a vague idea about what the API should looks like ?

[sbernard31]

This could maybe also used to support a more robust bootstrap session at client side. (see OpenMobileAlliance/OMA_LwM2M_for_Developers#523)