Add example configuration for Motion

In the same manner as with the general settings.cfg I have created a
copy of the motion.conf which will be used as a starting point when
configuring Security Cam for the first time. I expect further changes to
this example file.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Change file event trigger to on modified

Overriding the Watchdog method for on file created seemed to be
sufficient, but on the Raspberry Pi and with large snapshots, i.e. a
resolution of 1280x720 and with a size of around 50 KB, there is a
certain gap between file creation and last write to that file.

The result of that was the following: If the client requested a
snapshot, the server would invoke a snapshot creation. The file was
created and then the server immediately responded with a HTTP 200 OK,
but since the file was still empty the response contained no bytes and
no image could be decoded on the client side.

Hence, it was clear that the relevant method to override is on file
modified as this is invoked after the file stream is closed again. Also,
I have added an exception case for the try-clause in the server script.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Allow only one activity instance on the task stack

It was possible to create multiple instances of the main activity which
has the effect, that the user might have to press the *Back* button
multiple times until the application is closed eventually. This change
permits that more than one instance can be created.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Replace example motion configuration

Since I am starting to use the latest Motion build I am also replacing
the example motion configuration file. Although providing this file has
become questionable as each user should use the Motion configuration
file of the version installed on his/her machine.

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