Support a default converter for data read shell commands

The get and scan shell commands have the ability to specify some complicated syntax on how to encode the bytes read from HBase on a per-column basis. By default, bytes falling outside of a limited range of ASCII are just printed as hex.

It seems like the intent of these converts was to support conversion of certain numeric columns as a readable string (e.g. 1234).

However, if non-ascii encoded bytes are stored in the table (e.g. UTF-8 encoded bytes), we may want to treat all data we read as UTF-8 instead (e.g. if row+column+value are in Chinese). It would be onerous to require users to enumerate every column they're reading to parse as UTF-8 instead of the limited ascii range. We can provide an option to encode all values retrieved by the command.