RequestMemory: Add refresh method

[kfranqueiro]

This adds a refresh method which will instruct the store to
reload its data from either the existing server endpoint, or a new
endpoint passed to the method.

Inspired by http://stackoverflow.com/a/28756348/237950 because people shouldn't need to be that intimately familiar with Cache to do this.

Includes tests, doc update, and some improved comments.

(Note: the diff here might make it look like this strips a newline-at-EOF... actually, there were two trailing newlines, and it strips one of them.)

[kfranqueiro]

The person who asked the original question on SO pointed out that calling invalidate does not actually flush the cache store - i.e., any items from the old data that are not also present in the new data will still persist.

For the typical case where the cache store is Memory, we could call setData([]), but IINM it's technically possible to pass in your own cacheStore which could be something else, so I'm not sure that's a safe assumption.

I guess we could seriously iterate through the items and call remove as well, but that seems pretty onerous. Thoughts?

[RoyTinker]

I'm struggling with this issue now. I want to reload a dgrid with different URL parameters when a user selects a different option in a drop-down menu.

That scenario is really easy in ExtJS:

store.setBaseParam('someParameter', someValue);
store.reload();

[Newan]

works for me

Update Patch is very useful

[kfranqueiro]

@TimTheTinker FYI, regarding the SingleQuery mixin in the tutorial, we had identified a bug a few months ago in that mixin which IIRC would cause behavior like what you describe. The code in the tutorial has been updated to include a renderArray method: http://dgrid.io/tutorials/0.4/single_query/.

I'm surprised that the same thing happens in OnDemandGrid though, as I thought I had been testing with that. I'll have to re-test when we have an opportunity to consider this in a future version of dstore.

[dylans]

Looks fine (needs a quick rebase).

[msssk]

Changes merged in #230