Add binary support to is base64

[jeffmontagna]

Issue

isBase64 in data-mate has the following issues:

• Assumes all encoded data is a string, i.e. binary data encoded is converted to a string which then fails the check.
• Does not check for base64 url

Changes

• Remove conversion to string when decoding value to check.
• Added base64Url and base64Url with padding checks. isBase64 returns true for base64, base64Url and base64Url with padding.