Adds filter to control max number of posts in query block

[willowCeleste]

This adds a filter that allows a dev to control the max number of posts allowed in the query block. I removed the old hardcoded attribute maxNumberOfPosts and replaced it with a new value which is passed into the block via wp_localize_script.

Fixes #114

[mboynes]

Code is 💯.

One outstanding question on this though, that I can't answer but maybe @mogmarsh can: by removing the attribute we eliminate the opportunity to add a UI control for this value. Is that OK? Is that something that would be valuable?

[mogmarsh]

@mboynes @willowCeleste
The original thought behind this was that a developer could set the maxNumberOfPosts and minNumberOfPosts in code - possibly in a template or a block theme, etc. and the end user would not see the attribute (unless they went into code view), but would be restricted in how many posts they could select on the front end.

For instance, the developer could say "you can have between 3 and 5 posts in this particular location", which gives the end user some flexibility, but not full control. If the minimum and maximum are set to the same number, the end user does not get any control, the range selector is not displayed.

I wonder if maybe we can leave support for maxNumberOfPosts and minNumberOfPosts but instead of setting the default value of maxNumberOfPosts to 10 we use the new localized value? I think that would allow for the original functionality, but also allow for a sitewide max.

[kevinfodness]

imo I'd rather not have the "invisible setting" and go with a sitewide max, and allow flexibility in use of the blocks.