Outsource algorithm to compute matrix power

[schillic]

See this thread.

Summary:

• Add an abstract type IntervalMatrixPowerAlgorithm.
• Add a field algorithm::IntervalMatrixPowerAlgorithm to IntervalMatrixPower (best make this a type parameter).
• Add types for each algorithm and implement apply methods.

struct MultiplyAlgorithm <: IntervalMatrixPowerAlgorithm end
struct PowerAlgorithm <: IntervalMatrixPowerAlgorithm end
...