MUS-50 AddLogTags

Added Log-Tag member to each class (private static final String TAG) and changed each call to Log to provide the TAG member as first parameter. Added testcase LogTagTest to check each class for having a TAG-member and each call to LOG for using the member. 

Jenkins Testresults: 
https://jenkins.catrob.at/view/Musicdroid/job/Musicdroid-custom-branch/34/testReport/