Correct the SLF4J bindings in the pom.xml files

When the user executes:
bin/gora logmanager

the following warnings are displayed:
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/apostolosgiannakidis/Desktop/MSc/MScProject/src/apache-gora-0.3/gora-tutorial/lib/slf4j-jdk14-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/apostolosgiannakidis/Desktop/MSc/MScProject/src/apache-gora-0.3/gora-tutorial/lib/slf4j-log4j12-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/apostolosgiannakidis/Desktop/MSc/MScProject/src/apache-gora-0.3/gora-tutorial/lib/slf4j-simple-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

It seems to be an issue with the pom.xml files; some exclusions should be added.