Add capability for adding and editing subsample tables

[khoroshevskyi]

• Add backed endpoint for editing subsample tables
• Add UI for editing subsample tables

p.s.
in raw peppy subsample_dict is a list (I probably named it incorrectly🫥) So we can have more then one subsample table.

[nleroy917]

I am close on this, but @khoroshevskyi, I'm getting a weird error from peppy when sending the subsample table data:

subsample_df = pd.DataFrame.from_dict(updated_project.subsample_table)
subsample_df_json = subsample_df.to_dict()

new_raw_project[SUBSAMPLE_RAW_DICT_KEY] = subsample_df_json
 new_raw_project[CONFIG_KEY] = current_project.config.to_dict()

new_project = Project().from_dict(new_raw_project)

>>> ValueError('DataFrame constructor not properly called!')

[khoroshevskyi]

Now, UI has only one subsample table. What if project will have multiple subsample tables? I think it's not high priority, but it would be nice to think about this issue

[khoroshevskyi]

Issue was partially solved. Subsample creation and modification on the UI was added (for one subsample table). Closing this, and opening separate issue: #208