Trainer train simplified, tests for load (#168)

- the arguments of Trainer.train now are passed to the fit
- unittest for load/restoring from checkpoint

pina/trainer.py

@@ -7,7 +7,7 @@ from .solvers.solver import SolverInterface
 
 class Trainer(pl.Trainer):
 
-    def __init__(self, solver, kwargs={}):
+    def __init__(self, solver, **kwargs):
         super().__init__(**kwargs)
         
         # get accellerator
@@ -29,6 +29,6 @@ class Trainer(pl.Trainer):
         self._loader = DummyLoader(solver.problem.input_pts, device) 
 
 
-    def train(self): # TODO add kwargs and lightining capabilities
-        return super().fit(self._model, self._loader)
+    def train(self, **kwargs): # TODO add kwargs and lightining capabilities
+        return super().fit(self._model, self._loader, **kwargs)