[CODEC-59] Add methods to Base64 which work with String instead of byte[]. Patch applied with one added test code line to keep line code coverage at 100%. Branch coverage up to 92% from 91%.
- Applied patch for [CODEC-81] production pretty much unchanged.
- Applied patch for [CODEC-81] tests and split one new unit test method into two tests. One for URL-safe and another for normal processing.
- Renamed StringBytesUtils to StringUtils
- Added missing @return tags to StringUtils