error handling for updates_for edge cases

[leastbad]

Two additions:

Component will now report that a url cannot be fetched, and abort with an error log with the failed url.

If there is a mismatch between the number of updates_for elements on the origin page and the url specified (or if the current page changes between updates!) this is handled as follows:

• if there are not enough elements to fulfill the updates, it will emit a warning log message
• if there are too many elements, the component will ignore the surplus

Originally, I was going to make it notify the developer that there were mroe data points than could be displayed; however, given the complexity of supporting multiple URLs, which could all have different amounts of numbers, I decided to take a pass on trying to create logic for the "too many" case.