Some regions using comma instead of dot for decimal point and users with comma cannot enter it

[nrsimha]

If user using region/keyboard where comma is used instead of dot (e.g. Czech, Slovak, Poland, ...) he is not able to enter decimal point as Regex to validate input firoAmount and fiatAmout requires dot as decimal point.

Issue is in lib/pages/wallet_view/send_view.dart on lines 768 and 855.

https://github.com/cypherstack/Campfire/blob/master/lib/pages/wallet_view/send_view.dart#L768
https://github.com/cypherstack/Campfire/blob/master/lib/pages/wallet_view/send_view.dart#L855