Add all Go types for the code generator of the sqlite engine

[philippta]

Based on the lose typing of SQLite and how the popular driver github.com/mattn/go-sqlite3 handles them, I've extended the sqlite codegen to generate the Go types accordingly.

This is the mapping of SQLite database types to Go types I cound figure out:

                 INT => int64
             INTEGER => int64
             TINYINT => int64
            SMALLINT => int64
           MEDIUMINT => int64
              BIGINT => int64
    UNSIGNED BIG INT => int64
                INT2 => int64
                INT8 => int64
           CHARACTER => string
             VARCHAR => string
   VARYING CHARACTER => string
               NCHAR => string
    NATIVE CHARACTER => string
            NVARCHAR => string
                TEXT => string
                CLOB => string
                BLOB => []uint8
                REAL => float64
              DOUBLE => float64
    DOUBLE PRECISION => float64
               FLOAT => float64
             NUMERIC => int64
             DECIMAL => int64
             BOOLEAN => bool
                DATE => time.Time
            DATETIME => time.Time
           TIMESTAMP => time.Time

Link: List of all supported SQLite types
Link: Type handling in the go-sqlite3 database driver

A small note on the integer type:

• SQLite does not enforce the size of integers, meaning that whenever a value exceeds the max value of an int32, it will automatically result in an int64.
• Because of that, github.com/mattn/go-sqlite3 will always use int64s.
• This is also the reason I've changed the already existing type for integers from int32 to int64.