Add flag to load identity file while dialling home

[Fahrj]

While I still want to clean up the code a little, this should already be a working solution for #20

@rucciva feel free to test!

Closes #20

[rucciva]

hi @Fahrj , how do i test this? do i need to compile it?

[rumpelsepp]

You could just checkout the branch 20-identity-file and build it.