Consolidate all db schema changes in a single file

Handle all schema migrations through a single switch statement
where updates fall through. No need for loops or magic function
invocations.

The schema for the initial database setup was reverse engineered
by taking the old schema_install.sql (which was equivalent to v2.36's
schema) and unapplying all older changes as relevant (column type
changes were ignored since they become no-ops)

While at it, fix support for table name prefix: Both the database
initialization and later update steps failed here.

After every version, the php timeout is reset to 300 seconds.
Nicer message on initial db install
enforce utf8 with mysql
defuse umlauts

Also add missing default wiki entry and
permission to see church service calendars
for the anonymous uesr.

With this commit, a new install is identical
to old style installs except for timestamps
and some row orders.