Layers and Models update PR

* add residual block
* add test conv and residual block
* modify FFN kwargs

pina/model/layers/fourier.py

@@ -0,0 +1,24 @@
+import torch
+import torch.nn as nn
+from ...utils import check_consistency
+
+
+class FourierBlock(nn.Module):
+    """Fourier block base class. Implementation of a fourier block.
+
+    .. seealso::
+
+        **Original reference**: Li, Zongyi, et al.
+        "Fourier neural operator for parametric partial
+        differential equations." arXiv preprint
+        arXiv:2010.08895 (2020)
+        <https://arxiv.org/abs/2010.08895.pdf>`_.
+
+    """
+
+    def __init__(self):
+        super().__init__()
+
+
+    def forward(self, x):
+        pass