Allow user to easily change between conventions in angular and barrier factor terms

[Thomas Latham]

Implement functions (probably in LauResonanceMaker) to allow the user to easily set in which frame the bachelor momentum should be calculated, whether or not the so-called covariant corrections should be applied, etc. Check also that things are sufficiently configurable for the form of the Blatt-Weisskopf factors, whether the momentum terms are ignored (i.e. the angular terms is just the pure Legendre polynomial), etc.

[Thomas Latham]

(In [401]) Implement expressions for the spin factor based on covariant tensor formalism Make it much simpler to switch between formalism options via new functions in LauResonanceMaker:

• setSpinFormalism, setBWType, setBWBachelorRestFrame
• default settings are unchanged (and are equivalent to setting LauAbsResonance::Zemach_P, LauBlattWeisskopfFactor::BWPrimeBarrier, LauBlattWeisskopfFactor::ResonanceFrame, respectively)

close #70