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'm not sure I agree with this. If the grid never has the full data set, then we can't perform an export(). I think this method should continue to function, with a warning to developers that their servers will need to either support this behavior, or detect it and reject it as an error.