Code cleanup

In this PR:

1. Globally replaced all instances of the variable config which refers to databaseConfig.js with variable dbcfg. This is more consistent and clear now that there is a mailcfg and mailConfig.js.
2. Modularized email/link generation subsystem; it is should now be trivial to generate verification links by importing components/Verify/verifySend.js. See that file for documentation.
3. Added email alert when a password is changed.