Adding libsdl2-image-dev dependency

Start session manager when not already running

Set version we're building from snapcraft

Make sure helper libraries get built as static libs

docs: build-android.md: Add missing step to initialise the build env

Make sure helper libraries get built as static libs regardless
of the cmake version being used.

This fixes issue 217.
Signed-off-by: NBernhard Rosenkränzer <bero@lindev.ch>

Warning currently prints out:

[WW 2017-05-03 15:15:30] [connection_creator.cpp:47@create_connection_for]
A second client tried to connect. Denied request as we already have oneand only allow a single client
                                                                       ^
Due to the way in which the code is formatted, we end up missing fudging
the words 'one' and 'and'.  Also the 3rd line in the source file seems
somewhat superfluous.  Let's fix that too.
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Setting up the build environment is a required step.

Without it, the subsequent step `lunch` will not be available.
Signed-off-by: NLee Jones <lee.jones@linaro.org>