Data validation

[petteripitkanen]

Data should be validated before it is written to PouchDB or Redux. There could be two layers, a PouchDB validation layer that would be used before documents are put to any PouchDB instance, and then a static layer that could be tested independently and that would be used by the PouchDB layer, in front of Redux, and also in the UI. UI should give clear warnings when there is something wrong with an edited document.