fix bug on request if transfert amount is 0

Conflicts:
	res/ui/mainwindow.ui
	src/cutecoin/gui/mainwindow.py

add about menu to open the about popup window

Refresh infos if referential is changed
Remove tab "parameters" to simplify UI

Conflicts:
	src/cutecoin/gui/currency_tab.py

Show members in table with columns for pubkey, uid, join date and expiration
Display members who will expire in 15 days as red

Conflicts:
	src/cutecoin/__init__.py
	src/cutecoin/core/wallet.py