Add external intent to enable offline mode.

I would like to use Tasker to enable synching of feeds before I go to work since I have a limited data plan. This commiit handles the intent extra "goOffline" to the OnlineActivity. When found, it will login then start downloading feeds/headlines as if the Offline button was selected. The difference is that no prompting is done from the user.

It also makes OnlineActivity a "singleTop" one so multiple instances don't "stack".

I'm kinda new to Android and Java coding and this could probably be better. For instance, duplication of the m_offlineModeStatus code in switchOffline() seems harder to maintain. Ah well, I hope this gets pulled anyway. :)

Thanks