Remove CalibrateRectangularDetectors and GetDetOffsetsMultiPeaks (master)

Because of compatibility reasons for wrongly fomatted data, omega scans
from D16 need to be loaded as histogram instead of point data. This
requires in turn some adjustements to existing algorithm using this kind
of data.

When loading metadata, check if a property is already present before
trying to add it, so that the loading can carry on with a simple warning
instead of failing altogether.

New DeprecatedAlias class to facilitate the renaming process of Mantid c++ algorithms

Add ability to rotate Ellipse and Rectangle shapes in Instrument Viewer Widget

Fix formatting of milestone link

--keep-going isn't available until sphinx 2.0
-W turns warnings into errors which should help jenkins figure out that
the build finished with warnings

Sphinx dev docs fixes