Slightly modified (improved) the database schema

Done changes?
	- The database now can control whether the `users`.`email` field is
	  not null
	- Also added `users`.`description` field for the new feature (user
	  is shortly describing himself)
Removal of deprecated change_profile_image() func
Introduced „profile information change“ functionality

Done changes?
	- created web/profile-edit.php
	- improved our „miscellanous functions“ library
Liquibase: Complete refactor of database changelog

From now developers should use current version of database-state.xml file
as the base for further development. This is the oldest correct version.
Introduced database changelog for testing data

Done changes?
	- created test-data.sql file - liquibase database changelog, used
	  to store test data for local development of DH
	- enclosed czech article about liquibase usage from
	  http://tom2ee-cs.blogspot.sk/2010/01/verzovani-datoveho-modelu-liquibase.html
Merge commit 'a3d3fd1' into profile
Merge branch 'profile' into dh-1.5

Conflicts:
	TODOlist.md