Add new method for converting user object

- method converts user to user with no emptyString values in object attributes
- use this in updateUser and updateNameTItles methods
- tested on postgreSQL and OracleDB
Fix default_data_quota module

- before this fix could be dataQuota set to unlimited even if limit was not unlimited
- now dataQuota can not be unlimited if limit is still limited
Merge pull request #302 from stavamichal/fix_update_user_for_oracle_use_null_instead_empty_strings

Add new method for converting user object

- method converts user to user with no emptyString values in object attributes
- use this in updateUser and updateNameTItles methods
- tested on postgreSQL and OracleDB
Merge pull request #307 from stavamichal/fix_default_data_quota

Fix default_data_quota module

- before this fix could be dataQuota set to unlimited even if limit was not unlimited
- now dataQuota can not be unlimited if limit is still limited
Merge branch 'engine-new-to-master-request' of https://github.com/mvocu/perun into engine_test