[Ovmsdev] Command prompt in secure mode

[Stephen Casner]

At Mark's request I have implemented a change to the command prompt
after switching to secure mode:

OVMS > ena
Password:
Secure mode
OVMS #

As implemented in this commit, the color also changes from green to
red, but that is only a proposal.  I also looked at blue, but on my
terminal it's not so distinct from black.  If preferred, we can have
both modes be green.

Actually, as I thought about this, I wondered whether our console
welcome banner and prompt should be different from green since all the
info-level log messages are green.  But there are not many ANSI color
choices and they don't look the same on all terminals, so we can't get
carried away with this.

                                                        -- Steve