(CS) Add link to songs in agenda
Finalize 2.42
(Cal) Add some preconfiguration to permissions
(CS) Added textarea to agenda inputs for servicegroups
Some minor bugfixing in CS und CDB
Remove mysqli use

This replaces mysqli use with PDO hardcoded to mysql.
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