Rename columns to avoid SQL syntax error

[reshmabidikar]

Recently, an SQL syntax error has been reported. On further investigation, it was found that the error occurs since there are some database columns named value and value is a reserved keyword. So we need to rename the value column to something else like field_value. Also see #151.

As part of this change, we will need to provide a migration file for the customers here.

We will also need to update the database migration doc. See https://github.com/killbill/technical-support/issues/16.

[pierre]

Note that sending /*! SET SQL_MODE=(SELECT CONCAT(@@SQL_MODE,',ANSI_QUOTES')) */; as part of the query used to do the trick to allow value as a column name in the queries, but this does not always work anymore (e.g., on latest Aurora RDS).

[reshmabidikar]

Addressed in #154