Changes:
* Introduce Jan's beautifully documented $wgMinervaABSamplingRate
Set to 1 to A/B test 50% of the population
* Split out ambox template styles into a separate file referenced
by hacks.less
* Update cleanuptemplates setup script to consider two buckets
Test pages:
* Shqiponja_Partizane
* World_War_II_in_Albania
* Liberation_of_Tirana
* French_Consulate
* Abd_ar-Rahman_IV
* M109_howitzer
* Aimoin
* Transport_in_Brazil
* Transport_in_Cape_Verde
Bug: T191303
Change-Id: I8d11e655ccb847b7999e64dda57b225ad8b1c23a
