OPENIG-126 Use ForgeRock's own Base64 encoder/decoder

* Removes dependency on commons-codec
* Reuse Base64 from forgerock-util

git-svn-id: https://svn.forgerock.org/openig@221 dbb9e58e-28e6-4ce0-90e8-f11d9605b710
Style only: removes unused imports

git-svn-id: https://svn.forgerock.org/openig@222 dbb9e58e-28e6-4ce0-90e8-f11d9605b710