network-manager-applet: add basic AP support

Tested with gumstix overo as access point and connected windows pc and android
smartphone.

Note that there are are some settings available for AP which do not make sense - see
[1] for further details.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=734589#c6



Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>