Collaborative page sizing

[diegosalvi]

We should add a way to choose page sizing a collaborative way between paged "modules" (blink, brin, tables). Each module have and know his byte overhead per page and it is different from module to module.

Setting page size to a low value could lead to too much page overhead with high memory space wasted.

Each module should be queried to known his page overhead and page size should be x time bigger than maximum overhead (10 times? configurable).

We have another sysprop to handle page size. It should be used only if lower than minimum evaluted page size.