File upload and persistence extension

- index.html extended with form input
- pasta.html and pastalist.html show link to /file/{pasta.id}/{filename} path
- files are saved in pasta_data folder
- all data is now stored in pasta_data/database.json
- changed pastalist.html date format to exclude year
- added custom 404 error handler

templates/error.html

@@ -0,0 +1,10 @@
+{% include "header.html" %}
+<br>
+<h2>404</h2>
+<b>Not Found</b>
+<br>
+<br>
+<a href="/" > Go Home</a>
+<br>
+<br>
+{% include "footer.html" %}