FR: allow varchar in "column type" dropdown

[adrienne]

Currently we only have text, mediumtext, and number options. I'd really like to be able to have varchar available for when i know the data will be short; it's more efficient for indexing purposes.

[bartdigitalpulse]

Have the same issue, wanted to put an index on this field but not possible with blob/text. I could force it in the migration but I assume this could have undesired consequences.