simple slicer to circumvent the 10k limit

[ArnarTumi]

This is a proposed fix to circumvent the 10k limit on a single entity in an Algolia search index. Since each entity can only be 10k in size, you get a rejection when trying to index large streamfields. This adds a basic slicer that slices the page content into < 10k chunks and appends a suffix to the objectID. Since the number of entities in an index is not a problem you can then add all those chunks as seperate entities and use distinct to prevent duplicates in search results.