MNE Browse Raw QT

New features:
+ Manual set events in the event list ar enow editable
+ Event list can now be filtered by event type
+ User can now build his own filter (lowpass, highpass, bandpass)
+ The implemented filter plot can be used to check the filter's frequency properties
+ User can export the designed filter coefficients to txt
+ User can export filter plot to png/svg file

Upcoming / Next Steps:
+ Implement projections
+ Lyout/Channel selection