ENH mne_experiment:  add .next() method to move through field values
ENH mne_experiment:  more rejection options

- use `kind` entry as primary option
- allow "make" (made by the user but not with rejection GUI)
STY mne_experiment.list_files()
ENH mne_experiment:  add .make_raw() with some defaults
ENH mne_experiment.make_epoch_selection():  automatically specify mad channels
ENH mne_experiment:  add make option to .get()
FIX mne_experiment:  test name should include cov
FIX mne_experiment: ttests
ENH mne_experiment:  add 'rnd-file' template for stimulus randomization
ENH mne_experiment:  update more .load_x() methods to load groups
ENH plot ndvar:  add Xax and ds arg to all plotting functions
ENH Sensor dim:  add x, y and z properties
API tests/tables:  break up analyze package and make top level modules test, testnd and table
FIX plot.sensor:  marking ROI (&TEST)
ENH datasets:  get_rand() to replace other dataset constructors
WIPDOC/ENH plot:  unified subplot layout for most plots (&TESTs)
WIP plot:  adapt kwargs of plots not adopting layout yet
ENH SelectEpochs:  page turning with arrow keys; show busy cursor
ENH SelectEpochs:  .auto_reject() method with more options
ENH ndvar:  __init__ ravel arrays as long as they are 1 dimensional