allow to connect to one server only

This changeset allow to disable block headers retrieval from multiple
servers.
dust threshold
fix label editing in gtk
add address type to receive tab in GTK GUI

I = imported
R = receive
C = change
network button fix for not connected to a network - GTK gui
add F and P to address types in recv tab for Frozen and Prioritized addresses
Merge pull request #379 from wozz/clean

label editing in gtk
don't show actinos that require private key if the wallet has no seed
concealed flag for restore sequence
fix: store seed version
Merge pull request #381 from atweiden/concealed-flag

concealed flag for restore sequence
call check_seed in get_seed
Merge branch 'master' of git://github.com/spesmilo/electrum
Update default server list (disable servers with failed/expired certs)
ignore gui/icons_rc.py
replace BaseException with Exception
don't use bare except
Merge pull request #385 from WyseNynja/ignore_gui_icons

ignore gui/icons_rc.py
Merge pull request #386 from WyseNynja/dont_use_base_exception

replace BaseException with Exception
wallet.py: use get_seed in update_password