Issues with adding defaults and attributes

[robcarey]

• when adding "CURRENT_TIMESTAMP" as the default value to a datetime or timestamp field, this does not get reflected in the schema or table build
• According to a note on https://modx.com/blog/2015/12/16/writing-xpdo-schema/ we should be able to add options such as "ON UPDATE CURRENT TIMESTAMP" to the attributes of a schema. Only 10 characters are currently able to save on the Extrabuilder attributes column. When manually expanding that limit to test, the value ""ON UPDATE CURRENT TIMESTAMP" can be saved, however, it does not get reflected in the schema or table build.
• anything saved in the "generated" field causes the schema build to not generate correctly. Some docs on this field and it's possible contents would be helpful.
• anything saved in the "extra" field shows up under a "generated" attribute in the schema. Possibly reversed with above? Some docs on this field and it's possible contents would be helpful. No obvious documentation is clearly visible when searching MySQL docs for "Extra"