Fix activities package typo

There was a typo with the activities package. This commit fixes that by
renaming it.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Implement just-once instruction activity

In order to avoid confusion about how this application works I have
implemented a launcher activity which displays instructions. The user
can either select 'Continue' or 'Exit'. If the user selects 'Continue'
then the instruction will not be shown anymore.

By using a translucent and no title bar theme the activity will not be
noticed on further application starts.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Adjust layout files to a naming convention

Just decided to choose the naming convention to prefix activity layout
files with activity_ and thus I had to adjust the main layout file.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Enable detection stop during snapshot loading

As described in issue #3 I need the functionality to stop the motion
detection while the current snapshot is still loading. Sometimes the
mobile internet connection is just too slow when all I want is to
shutdown the system before I enter my apartment.

This was done by adding task cancellation to the detection state and
enabling the toggle button when the interface is set to the detection
mode. Hence, this commit fixes #3.

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