Manage closed channels on open stations

see :

• http://resif-waveqc-dev.u-ga.fr/stations/12/
• http://resif-waveqc-dev.u-ga.fr/stations/25/
• http://resif-waveqc-dev.u-ga.fr/stations/114/

Station is still open but some channels have been closed.

• we should mark these channels as closed and display a black cell in station detail
• we should mark these channels as closed and display a black cell in network_full_detail
• we shouldn't mark the station as problematic in network_detail view
• we shouldn't mark the station as problematic in homepage
• improve fix_closes_channels_check
• improve update_channels