internal: Move transport/display.go into bridge package

[Jacalz]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

For some reason (probably due to how the old transport backend was put together), I placed the code for showing text send and receive windows in the internal/transport package as part of the client. This makes very little sense now that the coupling to the client struct is quite minimal.

• Move textSendWindow into ui/send.go.
• Move textRecvWindow into ui/recv.go.
• Embed the types into the corresponding send and recv structs instead of pointers (allocating the memory inline as much as possible.)

Describe the solution you'd like to see.

Moving the sending code out of the transport package should not be too big of a deal. The receiving end might be a bit trickier.

[Jacalz]

Actually: It might make more sense to move it into bridge.