ACTIVEMQ6-3 renaming directories from activemq6 to activemq

https://issues.apache.org/jira/browse/ACTIVEMQ6-3

We are renaming packages from activemq6 to activemq as that's more generic and version independent
On this first commit I'm just renaming the directories otherwise the history would be lost. The next commit will rename the text on the directories.
If I squash these two commits git will make us delete / add again.
ACTIVEMQ6-3 renaming package names from activemq6 to activemq

https://issues.apache.org/jira/browse/ACTIVEMQ6-3

We are renaming packages from activemq6 to activemq as that's more generic and version independent
The previous commit renamed the directories. On this commit now I'm changing the code.
If we changed the code and the directories on the same commit git would remove and add a lot of files
without recognizing the renames.