Support transactional IConfigStores

[maelgrove]

I've asked about this quite a while back (basically, why is there no Save method - and there are quite a few other issues covering this topic) and you answered me that there is no support for transactional configuration stores because some configuration stores are already transactional, which I can agree upon. Though it would still be nice to have some way to explicitly save the current configuration, for which I suggest the following implementation:

• There will be a marker interface called ITransactionalConfigStore which would inherit the IConfigStore contract and provide additional methods such as SaveChanges, HasUnsavedChanges etc. Only configuration stores which actually support this would implement the contract.
• The library would offer static accessors to each method, something like ConfigStore.Save<T>() which would trigger saving all configuration stores implementing this contract.
• An additional abstract type should be provided called AsyncConfigStore which periodically saves the current configuration in an asychronous manner.

[aloneguid]

I totally see your point. I think one can implement transactions outside of the stores themselves, inside the core library, as long as store interface supports batched save.