* Update the minimum bot token length to 58 char

- Updates the minimum length of a bot token to be 58 characters. An older 58 char bot token was found by Moiph
- Makes this value an internal const instead of a magic number

* update the TokenUtils tests for 58 char min

* Add input validation for bot tokens based on their length

* Add token validation to BaseDiscordClient#LoginAsync

Adds a TokenUtils class which is used to validate that tokens are correct

* Revert changes to DiscordRestApiClient

* Add Unit tests to the TokenUtils class, fix a logic error that was caught by those tests

* Allow for API to throw exceptions

Moves the validation of tokens to be inside of LoginInternalAsync, and writes a Warning to the console when the supplied tokens are invalid