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
Actually, do we need the `infinitePageSize` param at all? Can't developers just control this limit inside their remote fetcher? I think the grid should accept any page size returned back from the server in 'infinite' mode.