feat(network): Move network info -> network show native-token and gas-costs

[matevz]

network info seems out of place and ambiguous to network show.

This PR:

• splits network info and moves it under network show native-token and network show gas-costs,
• some minor pretty printing fixes

Example:

$ oasis network show native-token
Network:                  testnet
Token's ticker symbol:    TEST
Token's base-10 exponent: 9
Total supply:             9999999997.0 TEST
Common pool:              1387287547.112344642 TEST
Last block fees:          0.0 TEST
Governance deposits:      0.0 TEST
Debonding interval:       336 epoch(s)

=== STAKING THRESHOLDS ===
  entity:             100.0 TEST
  node-validator:     100.0 TEST
  node-compute:       100.0 TEST
  node-keymanager:    100.0 TEST
  runtime-compute:    10000.0 TEST
  runtime-keymanager: 10000.0 TEST

$ oasis network show gas-costs
Gas costs for network testnet:
  - reclaim_escrow:            1000
  - amend_commission_schedule: 1000
  - burn:                      1000
  - allow:                     1000
  - transfer:                  1000
  - withdraw:                  1000
  - add_escrow:                1000