Provide a command ‘hydra-init’ to initialise/upgrade the database

For schema upgrades, hydra-init executes the files
src/sql/upgrade-<N>.sql, each of which upgrades the schema from
version N-1 to N.  The upgrades are wrapped in a transaction.

src/sql/Makefile.am

@@ -1,6 +1,6 @@
 EXTRA_DIST = hydra.sql hydra-postgresql.sql hydra-sqlite.sql
 
-sqldir = $(datadir)/hydra/sql
+sqldir = $(libexecdir)/hydra/sql
 nobase_sql_DATA = $(EXTRA_DIST)
 
 hydra-postgresql.sql: hydra.sql

src/sql/hydra.sql

@@ -3,8 +3,6 @@ create table SchemaVersion (
     version       integer not null
 );
 
-insert into SchemaVersion (version) values (1);
-
 
 create table Users (
     userName      text primary key not null,