Use fully-qualified names in server functions

[sbellware]

per: #42

Once the category-level write lock is remediated in the next major version of Message DB, it will no longer be necessary to permit overriding the write lock function using alternative versions provided via Postgres' search path. At that point, the server functions can be more explicit in qualifying the server function calls by qualifying them with the message_store prefix.

[lgazo]

Why is the prefix/schema even required to be directly within the scripts? Wouldn't it be easier to omit the schema or template it?