open_genesis_config should return a human-friendly error

[james-chf]

Give a slightly better error message when anomac or anomaw commands are run, but a chain hasn't been joined. Before we would just get No such file or directory (os error 2), now we should indicate that specifically we can't read a genesis config file.

mbp> target/debug/anomac epoch
2022-07-07T16:58:56.136364Z  INFO anoma_apps::cli::context: Chain ID: anoma-internal.000000000000000
Error: 
   0: couldn't read genesis config file from .anoma/anoma-internal.000000000000000.toml
   1: No such file or directory (os error 2)

Location:
   apps/src/lib/config/genesis.rs:601

Backtrace omitted.
Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.
[1] - 2022-07-07 17:58:56

This PR also makes some changes such that we can propagate an error all the way back up to main() of anomac, anoman, anomaw, so that it will be easier in the future to propagate errors like this. (Relates to anoma/anoma#1049)

To close anoma/namada#97, we should catch the error and translate it to a friendly message such as one indicating to the user to join a network first, rather than panicking with a backtrace.

[tzemanovic]

moved to anoma/namada#291