Automatize Tutorials html, py files creation (#496)

* workflow to export tutorials

---------

tutorials/tutorial1/tutorial.ipynb

@@ -87,25 +87,27 @@
    "source": [
     "## routine needed to run the notebook on Google Colab\n",
     "try:\n",
-    "  import google.colab\n",
-    "  IN_COLAB = True\n",
+    "    import google.colab\n",
+    "\n",
+    "    IN_COLAB = True\n",
     "except:\n",
-    "  IN_COLAB = False\n",
+    "    IN_COLAB = False\n",
     "if IN_COLAB:\n",
-    "  !pip install \"pina-mathlab\"\n",
+    "    !pip install \"pina-mathlab\"\n",
     "\n",
     "import warnings\n",
     "\n",
     "from pina.problem import SpatialProblem, TimeDependentProblem\n",
     "from pina.domain import CartesianDomain\n",
     "\n",
-    "warnings.filterwarnings('ignore')\n",
+    "warnings.filterwarnings(\"ignore\")\n",
+    "\n",
     "\n",
     "class TimeSpaceODE(SpatialProblem, TimeDependentProblem):\n",
-    "    \n",
-    "    output_variables = ['u']\n",
-    "    spatial_domain = CartesianDomain({'x': [0, 1]})\n",
-    "    temporal_domain = CartesianDomain({'t': [0, 1]})\n",
+    "\n",
+    "    output_variables = [\"u\"]\n",
+    "    spatial_domain = CartesianDomain({\"x\": [0, 1]})\n",
+    "    temporal_domain = CartesianDomain({\"t\": [0, 1]})\n",
     "\n",
     "    # other stuff ..."
    ]
@@ -152,6 +154,7 @@
     "from pina.domain import CartesianDomain\n",
     "from pina.equation import Equation, FixedValue\n",
     "\n",
+    "\n",
     "# defining the ode equation\n",
     "def ode_equation(input_, output_):\n",
     "\n",
@@ -164,6 +167,7 @@
     "    # calculate the residual and return it\n",
     "    return u_x - u\n",
     "\n",
+    "\n",
     "class SimpleODE(SpatialProblem):\n",
     "\n",
     "    output_variables = [\"u\"]\n",