Rewrite using fputcsv() and single query to fetch rows

Made a partial rewrite of module. Changes:

• Use fputcsv() function, it should resolve most problems with broken CSV formatting.
• Fetch rows for CSV file with single query (including all profile fields). Tested it with MySQL only, probably it will be incompatible with PostgreSQL.
• Write rows to temporary file first and then transfer it to user. Module no longer needs 750Mb memory limit.
• Change path of admin page to /admin/user/profile-csv, added "Download CSV" to the admin page in addition to old download path.
• Move most code outside of .module file
• Add filter to fetch users registered within specified period

Update function from the last version is missing. But I'll make it if maintainer agree to commit new version.