Remove WaitState and restructure snapshot queries

As hinted in the previous commit I have removed the wait state from the
client, not only the model state, but also the controller state. Taking
on this I once more restructured the times when snapshot queries are
issued.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add GCM Sender ID to the preferences

Until now the GCM Sender ID was hard coded as a string. I have removed
that constant from the main activity and added another option to the
shared preferences which can be filled in the settings activity.

Also I have replaced the super constructor in GCMIntentService with a
no-args constructor. Now the sender ID is passed by the overridden
method getSenderIds.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Start refactoring main activity

I am now getting into the process of finishing off the first version of
this project. Hence, I have started to refactoring the classes. I start
with the main activity and have added some more comments, removed some
fields and started to reorder the methods.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>