po: Remove dead files from POTFILES.skip

https://bugzilla.gnome.org/show_bug.cgi?id=719358
applet: Remove applet code

It's not needed anymore, as gnome-shell can use the code
in GnomeBluetoothClient.

See https://bugzilla.gnome.org/show_bug.cgi?id=719341

https://bugzilla.gnome.org/show_bug.cgi?id=719358
lib: Fix weird GI enum names for columns

Move _BLUETOOTH_NUM_COLUMNS outside the enum so that the prefixes
are correctly stripped, eg. GnomeBluetooth.Column.DEFAULT not
GnomeBluetooth.Column.LUETOOTH_COLUMN_DEFAULT (yes, with the missing B)