Foundation for #41

* This commit introduces an estimated time of arrival (eta) to the
message status which helps to decide whether a message should be
retransmitted over a faster transport.

This also adds a script for makes upgrading dependency checksums so much easier

This only shows the settings if a screen lock is available.
If the setting is activated, it shows a drawer item for locking.
Once locked, the screen lock secret needs to be entered to enter the
app again.

First part of #1247