* support for count and aggregations on columns, close#786
* support explain query for aggregations
* '<arr-rel>_agg' in '<table>' type, fix order by for aggregations
* add 'allow_aggregations' key in select permissions
* Add checkbox to toggle count and aggregations on columns on select permission
* align aggregation checkbox with columns div
* improve readability of the generated sql
* alias is needed at the top level aggregation
* throw internal errors for unexpected fields
* rename SelFld to more readable TableAggFld
* rename agg to aggregate
Better SQL generation for select queries (the query plans will be the same but much more readable). This closes some long standing issues (#6, #121, #278).
This is breaking change where bigint and bigserial Postgres types will be encoded as GraphQL String types, as opposed to Int as present in earlier releases.
Input types were already encoded as String.
This is achieved by selecting `bigint` and `bigserial` columns as `text`s in the SQL query: `select "big_id"::text ..` instead of `select "big_id" .. `.
Reason for that change is outlined in #633 where JavaScript cannot decode 64 bit Integers.
