Added getBinaryResourceAsString() function

References #286
Renamed RetrieveResourceFromFtpServer unit test to
RetrieveBinaryResourceFromFtpServer

References #285
Improved _generateResourceElement() for FTP and SFTP classes

References #282
Added RetrieveTextResourceFromFtpServer

References #285
Renamed RetrieveResourceFromSftpServer to
RetrieveBinaryResourceFromSftpServer

References #285
Added RetrieveTextResourceFromSftpServer

References #285