BUG #13696. Enable the mobile plugin conditional on BUILD_SHARED_LIBS

On static build dashboards, the plugin creates a dock widget that
changes the size of the renderview, causing tests to fail.  So
the plugin will be disabled by default only for those builds.

Change-Id: Ib9eca3fa08e3f3b92b7fc41cf06357325fe144b5
Merge topic '13696_mobile_remote_control_plugin' into next

df73e37 BUG #13696. Enable the mobile plugin conditional on BUILD_SHARED_LIBS