qml: refactor default namespaces
qml: trying a simple way to enable custom additional tags (working
commit)
qml: correcting skipping present namespaces
qml: changing structure of additional info

pick.additionals: AttribtDict with field names as keys and dicts
containing "value" and "namespace"
qml: allow custom namespaces with and without given abbreviation. use

default obspy namespace when no namespace is given. currently looks up
fields in an AttribDict called obj.extra. Currently for pick and event
only.
qml: Added support for attributes in extra
update credits sorting order
temprorary fix for tutorial doing seismometer correction based on old
IRIS web services. Whole section needs refactoring.. :(
add Bode plot to Response object
changelog
Response plot: add line cross for instrument sensitivity
response plot: changes to call parameters

- more intuitive for users to be able to specify sampling rate +
  frequency step (i.e. min/max/step of frequencies) in plot (rather than
  t_samp and nfft)
- make it able to provide two axes for the plotting instead of making a
  new figure (will be used in plotting multiple channels in
  Station/Network/Inventory)
response plot for Channel class
Response/Channel plot: make it possible to pass in label string for
legend
Station plot: response plot working but might need some more work..
Station.plot(): only leave option to plot response

makes it simpler and clearer, for a map location plot it is probably
easier to nest the station into a network and use that for plotting
Station.plot(): take location codes into account
Merge remote-tracking branch 'upstream/master' into station_plots_master
station class plots: add example plots to docs
station type plots: fix plotting grid (just `grid()` toggles grid state)