Confusing copy / paste behavior for localized numbers

If you select a region setting with `,` as decimal separator, Postico tries to convert numbers automatically to a format compatible with PostgreSQL (using `.` as decimal separator) when copy / pasting tabular data.

This should make it easier to copy data between other apps like Excel or Numbers and Postico.

This means if you copy data like this

Price (source)|
----:|
0,99|
1.199,99|

Then Postico converts it to this:

Price (converted)|
---:|
0.99|
1199.99|

However if you paste something that is already using `.` then Postico thinks this is a grouping character and removes it resulting in wrong values:

Price (source)|
---:|
0.99|
1199.99|

Price (converted)|
---:|
99|
119999|

This is most certainly not what the user wants, and we should try to detect this and at the very least show a warning if something like this happens!

(You can confirm this behavior by copy/pasting from these tables)

Start by reproducing the copy/paste behavior with comma-decimal and dot-decimal values under a comma-decimal region setting, using the tables in the issue. Trace the tabular-number conversion entry point; done means dot-decimal values remain unchanged, comma-decimal values still convert correctly, and ambiguous conversions produce the requested warning.

Written by the indexing model from the issue text.