Added pagination style "infinite"

- Added the ability to use fetchers that do not implement a count() method. The property "paginationStyle" as suggested in #120 must be set to "infinite" to allow fetchers without
a count method.

- Added the option "infinitePageSize" to control the amount of data that should be retrieved an each scroll event. If undefined defaults to the amount of rows that fit into one viewPort page

- Modified some checks, so the fetchers without count methods can work without having placeholders in the table
I think we need an additional parameter in here to control when the next page should be fetched during infinite loading. Loading the next page right at the very bottom isn't ideal because it causes the user to have to wait. Ideally, the next page should get loaded before the user has finished scrolling to the bottom. The row offset should be a parameter, where 0 will be the current behavior, but 20 will cause the remote fetcher to fetch the next page when you're < 20 rows away from the bottom.