client and tls-client without pull

[hannesm]

in the rise of #129, we should figure out what to support / not support. the story unfolds:

• there's a static client (with static keys and static IP addresses), where nothing dynamic is used from the server
• there can be partially dynamic clients: i.e. do tls auth & authentication, then use NCP for cipher selection [or no NCP], but have the ip address configuration hardcoded in the configuration file [this still requires a push-request / push-reply to figure out the cipher -- unless there's no NCP used] (as far as i can tell)
• the multi-client server: here the client receives its ip configuration from the server (and thus a push_request / push_reply is needed for ip configuration)

it looks like the second case is not supported by miragevpn -- in case we find such a deployed configuration, we should re-evaluate. see as well #129 (comment) #129 (comment) for previous discussions).

[hannesm]

related is #92