Revert "Added a signin page (unfinished)"

This reverts commit 4613bf9824046fef073eed10bbf697293855bb59.
Revert "Prepared Users database"

This reverts commit 93144bc3752158bec5b92a7c09bcb557222ab33b.
Revert "Corrected missing password error message; added tests for error messages; refactored Flash tag"

This reverts commit 06a2e10322020e92c910625165988f92a95b2503.