add dmsgpty to skywire-cli

[0pcom]

add dmsgpty-cli and dmsgpty-ui comands to skywire-cli.

This PR depends on:
skycoin/dmsg#101

I've been able to test this by manually changing the dependencies to reflect the pull request in dmsg.
The dmsgpty-cli works, but the dmsgpty-ui does not register as a command, yet there are no errors or any indication why it does not appear.

The ability to launch the dmsgpty-ui from skywire-cli would be nice but is not essential for my purposes

dmsgpty-cli has been missing from skywire-cli; currently dmsgpty-ui is included with the visor.
this is a necessary step for further integration of update functionality into skywire-cli.

Changes:

• add dmsgpty commands

How to test this PR:

skywire-cli visor dmsgpty-cli

[jdknives]

@0pcom just gave this a run and it will not work as is:

• dmsgpty cli expects a config file to connect to the dmsgpty host
• the dmsgpty config is not the same as the config file we use in skywire

We do not currently generate a dmsgpty config in Skywire when running a visor (or when configuring a visor). We just take various values we need from the main config in Skywire and pass them to dmsgpty.

I would not like to add support in dmsg for the Skywire config as dmsg should be independent of Skywire completely. So we should add support for it in Skywire repo.