Don't use common diretory for different events.

Before the directory structure looked like this:
```
/tmp/periodicnoise/event1/event1.lock
/tmp/periodicnoise/event2/event2.lock
```
Which leads to problems, if different users use the tool. 

I see two possible ways to fix this:
a) use a permissions 1777 to create the directory. But this leads to tmp file attacks, which is low risk but not required to risk
b) use different directory naming with one directory per event

I have chosen to implement b. So the new directory structure looks like this:
```
/tmp/periodicnoise-event1/event1.lock
/tmp/periodicnoise-event2/event2.lock
```