sql: introduce like stuff

User can now like topics, rules and comments.
All handled with a single check constraint and stored
in the like table with optional foreign keys.

Further fixes;

* made a simple hierarchically concept for comments
* fixed some names from tables

Works only with oracle so far, next step are triggers and sequences.

Signed-off-by: Alexander Christ <alex.christ@hotmail.de>
sql: add sequence and trigger

Add trigger for:
 * Comments
 * Like
 * User
 * Rule
 * Message
 * Topic

to let the primary key set automatically with each new insert.
Currently using one sequence for all, maybe we need more in the future...

Signed-off-by: Alexander Christ <alex.christ@hotmail.de>