SchemaBuilder: data types naming convention

Hi ikkez, I didn't have a chance to try your SchemaBuilder plugin before. That's good work!

I bring here a suggestion for renaming the numeric types. I find the naming convention quite confusing since INT8 is 8 bits, but INT16 is 32 bits. I suggest naming them according to the target storage length: INTxx = xx bits.
Therefore we would have INT8, INT16, INT32 and INT64.
Moreover I changed the pgsql type for INT8 to `smallint` since it's closer to `tinyint` than `integer`.