Italian translation improvements - by Pierlauro Sciarelli

default datetime picker's time to current time when field is blank

Allow primary keys with special characters in editable list view

allow primary keys with special characters in editable list view and add tests for it, also remove unnecessary db.create_all() in other tests

comment position is wrong

Add an argument to FileUploadField to disallow overwriting existing f…

Fixed #846, #808. Refactored JOIN logic so it now works with relationship properties instead of tables.

This is partially incompatible change - you will have to update your custom filters. `apply` method now
accepts additional `alias` argument. `alias` should be used to resolve column in query with specific JOIN path.

Long story short, old code which was looking like this:

```python
class MyFilter(SQLABaseFilter):
    def apply(self, query, value):
        return query.filter(self.column == value)
```

Should look like this:

```python
class MyFilter(SQLABaseFilter):
    def apply(self, query, value, alias=None):
        return query.filter(self.get_column(alias) == value)
```

Follow-up on issue #890

Resolves one of the issues documented in #890