Remove Proxies from the list once proxy patches are successfully merged.

Even Fedora is no longer shipping the WiMAX SDK, so it's likely we'll
eventually accidentally break some of the code in src/devices/wimax/
(if we haven't already). Discussion on the list showed a consensus for
dropping support for WiMAX.

So, remove the SDK checks from configure.ac, remove the WiMAX device
plugin and associated manager support, and deprecate all the APIs.

For compatibility reasons, it is still possible to create and save
WiMAX connections, to toggle the software WiMAX rfkill state, and to
change the "WIMAX" log level, although none of these have any effect,
since no NMDeviceWimax will ever be created.

nmcli was only compiling in support for most WiMAX operations when NM
as a whole was built with WiMAX support, so that code has been removed
now as well. (It is still possible to use nmcli to create and edit
WiMAX connections, but those connections will never be activatable.)

If you accidentally click on an wifi network in the menu, and you
don't know the password, and cancel, the connection always stuck
around and was available for autoconnection.  That's annoying, and
it's a few clicks to go delete them.  But better yet, we can
slightly repurpose the 'timestamp' property of connections to
determine whether or not they've been successfully connected in the
past; NM stores timestamps for all connections as of version 0.9.

So if a wifi connection hasn't ever been successful (which means it
has a timestamp in the timestamp cache, but that timestamp is zero),
don't try to autoconnect it.

Preloaded connections without a timestamp will still be autoconnected
at least once (as they always have) because they won't yet have a
timestamp in the timestamp cache.