Improve conditions and refactor dataset classes (#475)

* Reimplement conditions

* Refactor datasets and implement LabelBatch

---------

Co-authored-by: Dario Coscia <dariocos99@gmail.com>

tests/test_solver/test_garom.py

@@ -4,7 +4,7 @@ import torch.nn as nn
 import pytest
 from pina import Condition, LabelTensor
 from pina.solver import GAROM
-from pina.condition import InputOutputPointsCondition
+from pina.condition import InputTargetCondition
 from pina.problem import AbstractProblem
 from pina.model import FeedForward
 from pina.trainer import Trainer
@@ -16,8 +16,8 @@ class TensorProblem(AbstractProblem):
     output_variables = ['u']
     conditions = {
         'data': Condition(
-            output_points=torch.randn(50, 2),
-            input_points=torch.randn(50, 1))
+            target=torch.randn(50, 2),
+            input=torch.randn(50, 1))
     }
 
 
@@ -74,7 +74,7 @@ def test_constructor():
           generator=Generator(),
           discriminator=Discriminator())
     assert GAROM.accepted_conditions_types == (
-        InputOutputPointsCondition
+        InputTargetCondition
     )