Provides a checkbox in the settings view, as well as an event handler to
disable/enable the tor network if the device is not on using the wifi
connection.

Refactors network-enabling code to a separate function. This function
is ran after the network state changes, or the settings change and
will update the status accordingly.

and fix message divider background for lower API levels.

Closes #97

UI was transferred into XML files
and lots of redundant code was deleted such as the custom CodeEntryView.

Closes #33

Users were confused by the process of adding a contact for the first time.
This change adds additional explanation and a picture of what is going on.

It also moves part of the UI into XML files.

Closes #87

The text of the startup failure notification is unhelpful due to lack of
space. Touching the notification now launches an activity that gives details
of the problem and what can be done about it.

Closes #38

We don't need two separate executors for long-running IO threads.