[Android] Show UI indication when APRS is actively being transmitted #384
Description
There should be a UI indicator when an APRS message is being transmitted over the air.
Right now, we show a snackbar after the transmission for beacons, but on the APRS chat screen we don't show anything after the user hits send on a text chat message, or after they hit the pin icon to manually beacon their position. So it can look like it didn't work, and they may tap it multiple times resulting in re-transmits. Two changes should be done:
- Add a UI indicator as soon as tx is initiated, a simple snackbar is probably easiest, but we could alternatively show something in the chat box to show that it's pending.
- We should also disable the tx buttons (beacon and send text chat) until an active tx completes, so that dupes can't be sent unintentionally.