The new zoom implemented for ContinuousFunction is now factorized inside
Function to benefit the Sequence class. The same things is done to code
added to Graph::GraphController, which is moved into
FunctionGraphController.
This removes the reimplementation of several methods, most notably
computeYRange, as the implementation for function is general enough to
work on sequences.
Change-Id: I9b8211354064f46c3fa3dde3191dcb39d627a1d2