Change default RC limit to 10%, show more helpful error messages

[youkaicountry]

Resolves #182

Brief description

Changes the default rc limit to 10%, and gives more instructive error messages

Checklist

• [x] I have built this pull request locally
• [x] I have ran the unit tests locally
• [x] I have manually tested this pull request
• [x] I have reviewed my pull request
• [ ] I have added any relevant tests

Demonstration

(online) (unlocked) > rclimit .001
Set rc limit to 0.001

(online) (unlocked) > koin.transfer
missing parameter: to
Usage: koin.transfer <to:address> <amount:amount>

(online) (unlocked) > koin.transfer aaaa 1
cannot transfer, insufficient rc
Current RC limit: 0.001, RC available: 100
Try using a higher RC limit. Example: rclimit .002

(online) (unlocked) > rclimit .001%
Set rc limit to 0.001%

(online) (unlocked) > koin.transfer aaaa 1
cannot transfer, insufficient rc
Current rc limit: 0.001%
Try using a higher RC limit. Example: rclimit 0.002%