Further denomination-related improvements

[kostko]

Further denomination-related improvements:

• oasis paratime list should have another column DENOMINATION(S) containing comma-separated currencies, number of decimals and the default one marked with (*). For example EUROe[18] (*), TEST[18]
  Issue: oasis paratime list: Add column DENOMINATION(S) #236
• new subcommand oasis paratime denom with
  • add <network> <paratime> <denomination> <number_of_decimals>
    Issue: Add new subcmds denom set and denom set-native and denom remove  #241
  • remove <network> <paratime> <denomination>
    Issue: Add new subcmds denom set and denom set-native and denom remove  #241
  • in the future, other ERC-20 related operations will also be covered by the denom subcommand
• the list of registered denominations. This should probably go inside the oasis paratime show <paratime>

Originally posted by @matevz in #206 (review)