Add Timezone Field to User record

Plan: 1. remove "tz" column from PortalUser table 2. add TimeZone column (varchar(255)) into PortalUser table 3. use same control as for website timezone entering (2 dropdowns in a row) 4. display new TimeZone field on both user/admin editing screens in admin and on user registration/my profile forms on front-end 5. hide new TimeZone field from user/admin editing form by default via simple interface preset 6. in kApplication::ValidateLogin method do putenv('TZ=<time_zone_string_here>') ( [url] http://www.php.net/manual/ru/function.putenv.php#11811[/url]) only when user has selected his timezone. 7. all timestamps in db are always in UTC, so no additional timestamp processing except putenv is needed 8. create 2 users with different timezones (different from each other and from server) and verify that each of them properly sees dates (e.g. link submission date) from other user actions. 9. create user without a timezone set and verify that he still works as before this task implementation.