Mer: Do not de-configure projects on target addition

The shared targets.xml file is not updated atomically and thus the
change is received as all targets removal in the first step with all
open projects de-configured as a result.

[qtc] Do not de-configure projects on target addition. Fixes MER#811

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Merge pull request #13 from martyone/next

Mer: Do not de-configure projects on target addition
Merge pull request #14 from jlehtoranta/next

Adds sdktool with mer plugin support