Merge p300 process_raw and base paradigm process_raw

[jsosulski]

For some reason the process_raw method exists for base and p300 paradigms individually but both methods are highly similar. We should consider splitting the method and overwrite only a part of it in the p300.py file.

The current state makes writing patches somewhat tedious, as both locations in the code need to be updated simultaneously.

[jsosulski]

When diffing only the relevant code sections I get the following diff:

--- <base.py>
+++ <p300.py>
@@ -6,22 +6,22 @@
         if len(stim_channels) > 0:
             events = mne.find_events(raw, shortest_event=0, verbose=False)
         else:
-            try:
-                events, _ = mne.events_from_annotations(
-                    raw, event_id=event_id, verbose=False
-                )
-            except ValueError:
-                log.warning("No matching annotations in {}".format(raw.filenames))
-                return
+            events, _ = mne.events_from_annotations(raw, verbose=False)
+
+        channels = () if self.channels is None else self.channels

         # picks channels
-        if self.channels is None:
-            picks = mne.pick_types(raw.info, eeg=True, stim=False)
-        else:
-            picks = mne.pick_types(raw.info, stim=False, include=self.channels)
+        picks = mne.pick_types(raw.info, eeg=True, stim=False, include=channels)
+
+

         # pick events, based on event_id
         try:
+            if type(event_id["Target"]) is list and type(event_id["NonTarget"]) == list:
+                event_id_new = dict(Target=1, NonTarget=0)
+                events = mne.merge_events(events, event_id["Target"], 1)
+                events = mne.merge_events(events, event_id["NonTarget"], 0)
+                event_id = event_id_new
             events = mne.pick_events(events, include=list(event_id.values()))
         except RuntimeError:
             # skip raw if no event found
@@ -64,7 +64,6 @@
                 preload=True,
                 verbose=False,
                 picks=picks,
-                event_repeated="drop",
                 on_missing="ignore",
             )
             if bmin < tmin or bmax > tmax:

As far as I can tell only the part where Target/NonTarget events are picked are specific to P300. The remaining differences seem to be caused by updates to only one of the files, or is there another reason I do not see here @sylvchev ?