NSH: Add option to use platform-specific logic to verify login credentials; Add option to add a delay after each failed login attempt

nsh_stdsession() cannot use the same login logic as nsh_session(); Also put telnet login in a separate file for symmetry

apps/nshlib:  All NSH sessions may now be protected with passwords stored in the encrypted /etc/passwd file

NSH: Add logic for the case where the passwd file is read-only.  ROMFS image needs to be marked as const, or it will end up in RAM.

examples/qencoder: Add configuration options to Kconfig file

Revert "Revert "NSH: All nsh_output strings tagged with IOBJ so that they may be stored in FLASH on AVR""

This reverts commit fd083ee9.

This reverts commit 186a101d.

This reverts commit cb6a914d.

OS test: Mark some constants as long to avoid overflow when used the AVR8.  Example, 500*1000 overflows when type int is only 16-bits, but 500*1000L avoids the overflow