Error on missing plugin before unknown option

[spoonincode]

Change appbase to error out when seeing an unknown plugin before erroring out on an unknown option. Otherwise it’s a little confusing that the reason the option isn’t recognized is because the plugin simply doesn’t even exist.

To accomplish this, have to make two passes through config.ini. First pass just parses the plugin= statements and then makes sure those are all valid, second pass parses all options.

Keep in mind this doesn’t change behavior where you can set a plugin option and not activate said plugin. For example I can still put bnet-threads in my config.ini but this will not be an error even I forgot to activate eosio::bnet_plugin

[heifner]

@spoonincode Are you still interested in getting this change in. Seems like a good idea.