Deprecated tableize()

I vote for deprecating this method in 3.0 beta and remove it in 3.0 stable.
Since the main usage in 2.x was from Singular ModelName to plural table_name, this was fine.
But now the table classes are in plural and therefore this method does not really make much sense anymore.

We should rather use underscore() directly to go from table class (plural) to table name (also plural).